What is with this crazy computer?

I have had a Dell computer do this when the CMOS battery got low. Try pressing the F2 key when the computer boots up and going into the setup. Check to see if it recognizes that all of your drives (hard, CD, DVD) are in the system. If not, check the cables on all of those drives. Restart the machine and see what happens, sometimes it takes a minute or so for the BIOS to find and add all of the IDE devices. Once it figures it out again you should not have any more problems.