If you're using either Win 98 or 98SE and the problem happened in the last 5 days, then press and hold the Ctrl key during startup, select 'Command prompt only' from the menu using the arrow keys, press Enter, at the C:\> prompt type scanreg /restore, press Enter, select a Registry that predates the problem, and press Enter.
If you're using Win ME or XP, then do a system restore.
Also, update your AV program with the latest files and do a virus search, and remove any spyware with either Ad-aware or Spybot.
Actually, everything that can be accessed in My Computer can also be accessed in Windows Explorer and Control Panel.