IS THE SCREEN IMAGE MARRED BY THIN LINES OR TINY SPOTS?
Assuming somebody didn't draw perfectly straight lines on your screen with a very thin magic marker or apply dots with the same, these are symptoms of physical LCD failure. It's not liquid crystals themselves that fail, but the transistors that control their twist for individual pixels or address whole lines. The individual point failures may be tolerated if they aren't rapidly multiplying; it doesn't affect anything but your temper in terms of usability. Laptop manufacturers normally specify some smallish number of dead pixels after which they will change the LCD under warranty. The point pixel failure don't have to be dead black spots, they can fail "on" as well, meaning you'll always have a red, green or blue spot, which is more annoying than black on a white desktop. A thick line, or a large black (dead) bar all the way across or up and down the screen usually indicates that the ribbon connector is partially worked of the LCD panel or the main board. This happens frequently on some laptop lemons where the connector was poorly designed and the cable is too short, so any vibrations or flexing of the case tend to work it loose. If it's not a loose connection, it's likely that the contacts on the display edge have separated, which means replacing the whole LCD unit.
DOES THE LAPTOP DISPLAY A LIVE BIOS SPLASH SCREEN?
Most laptops will display a manufacturer splash screen with their brand name, Dell, Toshiba, Acer, Sony, etc, before launching into windows. Even those that don't should flash a text screen with the BIOS maker (AMI, Award, and Phoenix) in the corner, and a message telling you what key combination to use to access the BIOS Setup screens. A biometric screen prompting you to scan a fingerprint before the system will boot counts as a BIOS splash screen here. If the screen lights up with anything, a graphic or text, it means that the basic display I/O system is functioning.
IS THE LAPTOP DESKTOP LIVE ON AN EXTERNAL DISPLAY?
All notebooks should support an external monitor, usually with a high-density D-Shell 15 pin VGA connector, but some might feature a DVI connector instead. It's a vital part of laptop display troubleshooting to determine if a known good external monitor can be used. Newer laptops don't keep the external connector live by default, and some don't allow for simultaneous display on both the LCD and an external monitor. You can toggle between the notebook screen (which isn't working) and the external display with an Fn key combination. The Fn key is located at the lower left of the keyboard, normally between the CTRL and the ALT key. Toshiba uses Fn-F5 to toggle between the laptop LCD and an external display. IBM or Lenovo uses FN-F7, Acer varies with the model, using Fn-F5, Fn-F3, Fn-F8, Sony Fn-F7, Dell Fn-F8, HP or Compaq, Fn-F4. There are variations with the age of the laptop and not all manufacturers have standardized on a key combo across the whole range, but you can usually figure it out from the little graphics on the function keys that line the top of the keyboard.
CAN YOU HEAR A FAN OR HARD DRIVE SOUND?
If you can't get any life at all on the laptop LCD or the external display, it's entirely possible that the problem goes deeper than a video issue. Signs of life include the cooling fan blowing, the hard drive spinning up, any LED activity beyond the LED indicating AC power is attached or battery charging. If the system is powering up, even going through boot as you can often tell by the level of hard drive activity demonstrated by the sound or the hard drive LED flashing, with no life on the LCD or external monitor, you have a board level failure. It could be the video processor failed due to overheating, you can try taking apart and reassembling the laptop body on the chance there is a bus connector failure (it's only a possibility on some models), but you don't have to bother inspecting the wiring to to laptop screen or connections in the lid since the external monitor bypasses all of these.
IS THERE A DIM DESKTOP IMAGE VISIBLE ON THE LCD?
Can you see a ghost-like image of your desktop that is functional, ie, one that changes if you drag an icon, launch a program or disappears if you shut down. Standard LCDs produce very little visible light on their own, they require the Cold Cathode Fluorescent Light (CCFL) to light the screen from behind. The fluorescent tube is normally located at the top of the screen, and a bright reflective surface distributes the light across the back of the LCD, so it can shine through the liquid crystals of the liquid crystal display, which only transmit red, green or blue (RGB).
DID YOU TEST THE INVERTER AND WAS IT OPERATING?
Since inverters put out high voltage, high frequency (something below the broadcast AM band) current, you can't test them with the average handheld meter. It involves disassembling the screen, the inverter board is normally contained in the non-viewable area of the lid. If the inverter isn't putting out the proper high voltage, check the DC power into the inverter. If the power to the inverter is good but there's output, the inverter is bad, and can be repaired or replaced, If the output of the inverter is good and the backlight doesn't light, either the solder connections on the backlight have failed or the CCFL tube is burnt out. If you don't have the ability to test the inverter, you can still check that the power from the mainboard to the inverter is good, that the wire isn't pinched and broken in the hinge.
DID REDOING THE INTERNAL CONNECTIONS FIX THE PROBLEM?
If taking the laptop apart and redoing all of the plug-together connections in the lid and the back of the body fixes the problem, you're golden. If not, inspect the wire harness running through the hinge to the lid for any signs of damage. It is still possible that you have a dead backlight or inverter and you can't see a dim image on the screen due to the type of LCD used, a darker than normal plastic film or less than perfect vision. Otherwise, you're faced with total LCD failure or a board level problem in the video subsystem output to the internal screen, which is possibly a connector failure or a short in the cabling.
DOES THE LAPTOP BOOT WITHOUT DISPLAYING ANYTHING ON THE SCREEN?
If the desktop never appears and you're left looking at a blank screen, but you can hear the hard drive is working away or other usual start-up sounds, or see the activity on the hard drive or wireless LEDs, the system is booting but the display isn't functioning. Another test is to wait a minute, but in an audio CD, and see if the drive spins up and the music starts playing. If the laptop does boot up without displaying a live desktop, try toggling the keyboard switch to swap between internal and external monitor (Fn plus a Function key which usually has a tiny laptop and monitor pictured on it). Try booting in Safe Mode, though since you'll have to shut down blind using the power switch, there's a good chance the laptop will start in Safe Mode by itself the next power-up. If you still can't get a live desktop, you can try attaching an external monitor, and if it's live, the problem is a software setting forcing the OS to display on the external screen only after boot.
IS THE IMAGE DISPLAYED EITHER UPSIDE-DOWN OR BACKWARDS?
Many laptops have the ability to flip the display horizontally or vertically. On many models, the you can do this from the keyboard, on purpose or accidentally, by hitting CTRL-ALT and the appropriate arrow from the direction arrows on the right-hand side of the keyboard. If the key combination doesn't do it, the problem is in software, either in the video driver properties or a malicious mirror program installed to make you wonky.
CAN YOU SEE A RED OR AN ORANGE TINT, OR IS THE LIGHTING UNEVEN?
Is the entire screen tinted red or orange (probably growing worse over time) or is the background brightness of the screen uneven, particularly near the edges? The tin is caused by a failing backlight not putting out the full spectrum of white light, so the CCFL tube needs to be replaced. This can be a delicate job due to the latter problem, uneven lighting. The tube is very thin, flexible, and often installed underneath a reflective foil that wraps the whole back of the LCD panel. If the backlight tube is jolted or warped out of position, or if you install it poorly, you can end up with uneven lighting of the screen.
DOES THE DISPLAY SCRAMBLE WITH THE PROGRESSION OF TIME?
This is the classic symptom of an overheating video processor or memory problems. Most laptops share main memory with the CPU, but memory modules don't have to fail all at one so if you have multiple memory modules installed, you can try taking out the one that's socketed (small panel on the bottom of the laptop held by one or two screws) to see if that changes the display. Otherwise, your best bet is opening up the body of the notebook, removing the heatsink from the video processor and making sure there is enough thermal compound (or not too much!) and if equipped with a fan, that the fan is still turning. A video processor may also display these symptoms if the entire laptop is running too hot, due to failure of the main cooling fan, clogging or obstruction of the intake or exhaust vents, Make sure you are running the laptop on a flat surface, with some open space to all sides, and not on a soft surface like a bed. The problem may clear up when you run in a power saver mode on battery with the processing speed turned down. You can also try turning off hardware acceleration in the advanced properties of the video adapter in the operating system.
IS THERE A STAIN OR GROWING PLUME THAT IS ALWAYS VISIBLE WHEN THE LAPTOP IS ON?
If a blotch appears on the LCD that isn't due to having spit coffee on the screen or dirty fingerprints, and it grows over time, it's the physical failure of the glass sandwich, and can't be repaired. This might also appear like octopus ink being slowly injected into the screen, a sort of growing plume. The only cure is replacing the LCD.
DOES THE LAPTOP DISPLAY EXPERIENCE TOTAL BLACKOUTS AT RANDOM?
One possible cause of seemingly random, total blackouts, is a loose connection. However, before you take the body and the lid of the laptop apart and remake all of the connectors in the video subsystem, it's worth checking the more obvious culprits, like a screen saver set to "blank" and poor wake-up behavior, or the video getting toggled to a non-existent external monitor by a keyboard failure (or operator failure). Check the power saver settings as well, and try running on a different power profile for a while in case the one you have been using is corrupt. Likewise, try running on battery to see if the blackouts are an overheating issue, but that's unlikely if the screen returns to the point you left off with some judicious tapping or moving of the lid:-) If the problem isn't blackouts, but unfamiliar distortions to the display, such as multiple screens displayed, only part of the desktop visible or a very blurry image, these are all signs of the video resolution having been changed to a bad choice, one which doesn't match the physical size of the monitor. Change the video properties in the operating system back to native resolution of the LCD, usually the highest resolution and number of colors offered. If the problem is large icons or a change in font size, this is due to display property choices in the operating system or in the particular application showing the symptoms.