SCA virus
Beth,
Boot your 500 with a disk that you know isn't infected.
Go through all your bootable disks with a virus detection utility that can
catch the virus on the disk, rather than in the machine. If VIRUSOFF will
do that, great. If not, I'd recommend VIRUSX, which you'll find on this
forum. Separate the good ones from the infected ones.
Take the infected ones and use the INSTALL command to install a new boot
block. For example INSTALL DF1: will install a new boot block on the disk
in DF1:. That will take care of any boot block viruses that may be on those
disks. You'll have to be careful doing this with some games that use
non-standard boot blocks, but if the game boots up with that familiar blue
screen, then you're okay.
Hope that helps, Robert