My D & E drives have disappeared

Hi,

I installed software for a memory stick that used a USB port. At first I couldn't copy files to the stick, I re-installed the software and copied files, after which I discovered the removable drive had changed to C. When I removed the memory stick my D & E drives were not showing on My Computer. I re-booted my computer, the drives were showing on boot up but not on My Computer and when I've tried to locate them it says it can't find them! The message says something like: they cannot be located, either they are not installed or corrupted.

Please can you help? My operating system is Windows 98SE.

Thanks

Mary Brumby