Yesterday I talked about keeping your PC out of trouble. Today I have a few more tips.
Get Your Product Key
One day you're going to need to retrieve your product key for any one of a number of Windows programs -- specifically, XP or Vista, or any one of the Microsoft Office suites. The easiest way to save yourself a headache is to grab the latest version of the Magical Jelly Bean Keyfinder. The product's free and supported by donations.
Just Delete That Folder
If anyone (like me) suggests you delete a folder, but you're not sure if you should -- don't. Instead, rename it or move it to a new folder (mine's cleverly called "Dunno"). If after a week or two everything's still hunky-dory, blow away the folder.
System Restore Reverts
System Restore isn't perfect, but if I have trouble, I always restore my system to a previous iteration. System Restore isn't perfect, but I find it useful. If I have trouble, I just restore my system to a previous iteration. If that doesn't do any good, or even makes things worse, I can use the "Undo my last restoration" option (most people don't know it's there).

Internet Connection's Gone Awry
It happens to the best of PCs -- something snags the Windows Sockets and wrestles them to the ground. There are lots of fixes, some of them covered in a PC World video called How to Reset Your Net Connection.
My first attack, though, is with WinSock XP Fix, a not-very-elegant tool that restores the Winsock Registry entries.
Do you have a favorite tool -- and a smart trick -- to prevent or repair a PC problem? I'm all ears.
Belarc Advisor seems to list all your keys, plus check all your Windows XP hotfixes (maybe Vista too?), which is a nice bonus feature if you don't like having too many little utilities. :)
The title of your column is incorrect, Steve. These problems aren't PC-related, but Windows-related. It would be better if the title reflects this.
Greetz, Pjotr.
@Pjotr: You're right -- and I changed it. --Steve