My Monitor Has Color Issues or Suddenly Goes Blank (No Display)
You might have connected your monitor to your desktop without using the screws on your DVI or VGA cable to lock the connector into place. Your first troubleshooting step should be to disconnect and reconnect your cabling; after that, try using a different cable (or borrow one from a friend) to see whether you can resolve the issue easily and inexpensively.
If you've ruled out the cable as the source of the problem, turn your attention to the connector. Assuming that your graphics board or motherboard supports a different connection type, try switching to one of the other connectors: DVI, HDMI, DisplayPort, to see if that fixes the problem.
Turn off your PC's power, and unseat and then reseat your graphics board (if applicable) to see whether a loose PCI connection is causing your display woes. Funky colors on your monitor could be an early sign that your video card is overheating (or going bad). Check your card's fan (if applicable) to confirm that it is spinning freely; if it's caked with dust, turn of your computer, touch the fan with your finger to prevent it from spinning, and blast it with some compressed air.
It's a bit of a long shot, but (if you can see anything at all) you might try uninstalling your video drivers and then installing the latest version from your card's or motherboard's manufacturer. If your monitor is completely dark but your system sounds as though it's loading, your monitor could be shot (or it could be set to display the wrong connection type), your video card could be dead, your power supply could be misbehaving (if it supplies juice to the card, disconnect and reconnect it to see if that fixes things), or your SLI connector may be awry.
My System Randomly Restarts Without a Crash or a Blue Screen
Though not always helpful, the fabled Blue Screen of Death may offer a clue about the underlying problem. Completely random restarts (or spontaneous shutdowns) are a bit more vexing.
One possible explanation is that components within your system are overheating. You'd typically see a graphical abnormality if your graphics board were at fault, but not if your CPU or a hard drive were getting too hot. There are several ways to help keep your CPU cool: Clean your CPU cooler; add more fans to your case; clean the thermal paste off your CPU and reapply a fresh drop. If your hard drive is to blame--and it isn't failing outright--get additional air on it or clean the fan (or fan grills) already directly responsible for cooling it.
Your power supply may be on the verge of giving out, but there's no good way to test its overall stability without replacing it and seeing whether the problem then goes away. Another possibility is that your power supply simply can't handle your components at maximum load--if you're trying to run a severely underpowered PSU on a tri-SLI setup, for example, trying to play a resource-hungry game might cause your power supply to wave the white flag. Of course, it might just be that your power supply's cables are loose.
Yet another potential sticking point is memory. Try removing and reinserting memory modules to see whether the problems disappear. A system with dual-channel memory may have the minimum two memory modules. If so, move those modules to the alternative channel slots.
All in all, the likeliest source of trouble is something related to your PC's power supply--but again, generic issues like "computer resets with no warning" resist simple, one-approach-fixes-all solutions.
My Keyboard Isn't Working--Nothing I Type Comes Up on the Screen
If you're trying to use a USB keyboard before Windows boots up, make sure that you've enabled support for legacy USB devices within your BIOS settings.
If you use an ancient PS/2 keyboard, try jumping into Windows' Device Manager, uninstalling the appropriate PS/2 keyboard driver, and restarting your PC. It's also possible (but unlikely) that, somehow, your PS/2 ports got shut down via your motherboard BIOS.
For USB keyboard users, one easy trick worth trying is to switch the USB port you use for the connection. Shut down your system and move your keyboard's USB connector from the front of your case to one of the motherboard's USB ports, or vice versa. If you're using a USB 3.0 port, try switching to USB 2.0. In some instances, a keyboard with any USB 3.0 ports needs to have a USB 3.0 driver installed in order to work properly. If you have a ton of other USB devices plugged in to your system, see if unplugging a few of them improves the keyboard situation.
And, of course, if you're rocking a super-fancy game-centric keyboard, try uninstalling and reinstalling the drivers for your device.
My Computer Is Trapped in a Cycle of Continual Reboots, With Constant Blue Screens
When your computer becomes trapped in perma-boot land, we recommend thinking back to what you were doing immediately before you started experiencing the problem. Were you installing a new piece of hardware? A new driver? A new application?
If you can boot into Safe Mode (press F8 after your motherboard posts), do so and then attempt to reverse whatever you did just prior to your computer's freakout: Uninstall the new application; remove the new driver; or scan your system for malware (you never know). If you have Windows' built-in system restore feature enabled, you can roll your PC back to an earlier system restore point in an attempt to return it to normalcy.
If you have no idea what you might have done to upset your system, you have to decide whether to try to fix Windows with various random tricks (reinstalling drivers, uninstalling dubious applications, running chkdsk, and so on) or whether to spend your time in safe mode copying your mission-critical files to a separate drive. Once you're done, format your troublesome primary drive, reinstall Windows, and copy your files back to the drive.
If you can't get into safe mode before encountering a blue screen, you might want to pop your hard drive out of your desktop, replace it with a new hard drive, reinstall Windows to the blank drive, and then copy your critical files off of your old drive after-the-fact. If you still run into repeated BSODs even with a brand-new drive installed, you have an unknown hardware issue--perhaps memory, perhaps overheating--and it's time to roll up your shirt sleeves and get creative (or to head for the PC repair shop).
Something's Burning--My System Is Emitting a Strange and Unexpected Odor
Something is definitely wrong if odd odors are emanating from your PC's chassis. Possible causes of unpleasant smells include blown capacitors on your motherboard (time to start shopping) and a failing power-supply fan (time to start shopping). But the problem might be tied to secondary symptoms: Did your monitor's picture suddenly zip out at the same time that your nose put you on notice? Did your computer lock up? Did it spontaneously shut off?
Your goal is to identify the source of the smell with a particular part. Burning smells can indicate failure in a cooling system (connected to the power supply, video card, or CPU), but they can also develop when you attach a cable backward (often accompanied by a burst of flame), accidentally short your motherboard, or improperly adhere a heatsink to a particular part.
Also, be sure to give the insides of your computer a good cleaning--a gentle dusting might resolve the olfactory outrage.