You might try reinstalling Internet Explorer from
http://www.microsoft.com/windows/ie/default.mspx
If this doesn't work then call a local consultant and take your roommates to
small claims court if they refuse to pay. There are lots of things that
could be wrong, beginning with spyware, virus remnants, other software, and
changed security and privacy settings.
Then, move out (or kick out your roommates). You are obviously living with
dangerously irresponsible people who have no respect for (at the very least)
your belongings. Finally,
1. Keep your antivirus software up to date (weekly).
2. Keep your operating system up to date by going to Windows Update.
3. Use a password to log on to your computer and never give it to anyone.
4. Disable the Guest account.
5. Get a good two-way firewall like ZoneAlarm (the built-in firewall
doesn't protect you from programs on your machine which try to access the
internet in ways which you would not want if you knew about them).
6. Run Ad-Aware (or similar software) to clean the spyware off of your
machine (
http://www.lavasoftusa.com).
There is more that should be done to keep a Windows XP computer secure, but
this is a start. However, a qualified consultant can help.
