Safe Mode: How to practice Safe PC.
You really messed something up and now your Windows PC won't boot. Unless you want to stare at the BIOS Startup screen for the rest of your days, you have to try to get into the Windows desktop somehow, and the best way is to try and boot into Safe Mode.
Most computer users have no clue as to what Safe Mode is and don't know how to access it. The essence of Safe Mode is that is that it (usually) allows you to load XP and Vista with an absolutely minimal set of drivers and other pesky buggy software that might be preventing you from booting. Safe mode will (again usually) get you to a cut-down version of your Windows desktop that isn't good for doing much, but will generally allow you to remove the problematic software from your configuration, or using System Restore to get back to a time when your PC actually worked properly. You might be shocked when you see the low resolution that your desktop will show up as, but thank your lucky stars that you can get to it in the first place and don't complain.
Many "experts" advise running a whole bunch of diagnostic utilities including the System Configuration Utility while in Safe Mode. To that I say in my best Brooklyn accent, "fuggedaboutit!" The best single use for Safe Mode is to access System Restore. Go back far enough to when you hadn't yet installed or accessed whatever you have that's screwed you up, and then just don't reinstall or reaccess that. It seems simple, but some people are just so retentive that they have to understand each and every byte's effect on their overall Operating System, while I prefer to just pitch it into the Recycle Bin and be done with it once and for all.
To access Safe Mode, you need to repeatedly tap the F8 key after about one to ten seconds after you turn the computer on. This should be immediately after the initial BIOS beep sound but long before the Windows logo screen shows up. You will then be presented with a Menu list of options. Disregard anything but plain old Safe Mode as the other options that allow you network access or command line interface are only for 1337 geekizoids: You'll likely see something along the lines of:
Enable Boot Logging
Enable low-resolution video
Last Known Good Configuration
Directory Services Restore Mode
Disable automatic restart on system failure
Disable Driver Signature Enforcement
...and maybe a couple of other enigmatic commands. Avoid them like the plague as they will most likely screw up your system to the point where even Safe Mode won't help.
Also remember that if you have one of those weird keyboards with an F-lock key, you will likely have to press that key first before the F8 key will work.
You can always escape Safe Mode by clicking Start > Shutdown and choosing Restart. This will automatically start Windows back into Normal Mode, although you might find that if you still can't boot up you may want to choose to go back into Safe Mode until you resolve the problem.
Safe Mode can be the best way to practice Safe PC. Just don't try to do too much while you're in it. Concentrate on getting back to a point in your System Restore when your PC worked fine and let it go at that!