Multiple Aps "not responding" on XP

First, if you didn't check for viruses in Safe Mode, you should do that. Note that some viruses can hide themselves from your antivirus program in normal mode, so you really need to scan in Safe Mode. To get into Safe Mode when you first power up, hit F8 about once a second until you get the menu and select Safe Mode. Then run a full system scan.
-
If that fixes it, fine. If not, use System Restore to go back to a date prior to the beginning of the problem. To run System Restore, click Start -> Programs -> Accessories -> System Tools -> System Restore. Click the box that says Show more restore points.
-
You can check for corrupted system files. Open an administrator command prompt and run SFC if the above doesn't help. Click START, then type CMD in the search box, right-click CMD.EXE and click Run as administrator. Then from the command prompt type sfc /scannow.
`
When you get your system back in good working order, I urge you to back your system up to an external hard drive and make regular periodic updates to it.
-
I hope this helps. Good luck.

As another poster mentioned, do your scans for malware, specifically Malwarebytes in Safe mode...but Safe Mode With Networking, not just Safe Mode. Spybot will do nothing UNLESS you have the paid version, it is basically a wheel spinner. AVG free is a decent A/V software but doesn't have the R/T features of the subscription (paid) variant, so it is limited in fucntionality. Many of the feebie downloads are limited in function, if functional at all, lastly stay as far away as possible from anything alluding to fix/repair or do anything with your registry.