If you have multiple users, I would suggest that you first log in as the administrator, in safe mode by pressing F8 on bootup repeatedly and select safe mode, and run any antivirus and antispyware programs. Since, as the saying goes, you don't know for sure where anyone has been, a virus could have been picked up from anywhere. Once you feel that you are virus and spyware free then maybe someone else can help if you still have a problem.
Only a suggestion
Windows 98SE, computer is set up for multiple users, so we each have our own desktop. Lately, when a user tries to log onto their screen, sometimes two things happen- there are no icons, only captions, and also some items are missing from the taskbar. Other times, everything is normal. When the corrupted desktop appears, you have to restart to cure it. Any idea what's happening?