the "crap" that occured without a firewall is likely a few trojan viruses and spyware installed on your system.
Go to download.com and search for the following programs. Download them all. UPDATE them all in their menues, then press F8 while rebooting to go into safe mode, and run complete scans.
The programs you need are
AVG Free (anrivirus)
Spybot Search and Destroy
Ad-Aware SE
Download this program as well. It is specifically made to get rid of harmful programs. Make sure to get the free version, and remember to UPDATE it as well.
http://www.emsisoft.com/en/Before running scans, one by one in safe mode, defragment your hard drive.
Start, programs, accessories, system tools, defragment. Reboot and defragment again.
Now go to start, programs, accessories, windows explorer.
Double click "my computer" then right click "C:" and choose properties, tools, error checking, check now. Click both boxes, hit ok and reboot. This will check your hard drive for physical errors and fix them automatically. It can take a while so be patient.
After this, reboot and do another defragment.
See if that helps.
If not, try one last thing. A program called anticrash.
http://www.tucows.com/preview/269386.html Let it "automatically fix errors" on your system. If this doesn't work, you may need to use your XP CD to reformat. Unfortunately you will lose everything this way, so you should back up important stuff to CD first.