My Dell Dimension 4100 Computer has a very strange problem that I have finally isolated. At first I could not get to cmos (bios) setup, but only got message that I needed a boot floppy which I made and it did nothing. Finally I got into setup and found it was dropping the hard drive, i.e., it would first show it was there, but the next time when I ran setup, after unit failed to work, it showed that hard drive was not there. I changed memory sticks, but to no avail. Any ideas of how to correct?