Yes, a reboot is probably in order (why didn't you try a reboot before posting?)
Anyway, if you still have the problems you can do a repair install and if done correctly, you will not have to reinstall your programs. Two things you can try:
1) A Restore Point from just before the problem arose. This is the simplest method - but it may or may not help.
2) If System Restore doesn't do it, do a repair install. Boot to your XP CD and choose the second repair option. Soon after loading the inatallation program will recognize you already have XP installed and offer a repair option. Do not take the first repair option (it will drop you at the repair console). Two screens later you'll again be offered a repair choice - take this one (press "R"). XP will install on top of itself, so it will take about 20-40 minutes depending on your system.