It might be the disk is full, being old and 98. Try F8, safe mode, which loads minimal drivers, and check the contents of C.
A dead hard drive reads no drive found. Back up data, means it is working, but you are running out of space.
Open the contents of C, and delete unneeded files. Disk cleanup and other tools do not work in safe mode, go manual, Windows Explorer. Be sure to finish with empty recycle bin. Then shut down and try a normal restart. 15% empty is needed for defragmentation, below 5% things turn strange, I think you are there.
If you get a normal restart, go on a cookie hunt, get rid of everything, till you can run disk cleanup and defragmentation. Restart is not shut down, down, dead, then start.
As for programs, go to control panel, add remove programs, and uninstall, which is not the same as delete from Windows explorer, that just gets rid of the file, unstall goes deeper. Make sure you are running one internet program, and one antivirus, they do not play well with others. Do this first, then go to Windows explorer and remove the files, then desktop icons, start menu.
I have bought many computers from thrift stores, this works most of the time.