What was the cause of this (ie did you change something just before this happened)?

You could try resetting your BIOS to its 'optimised defaults' from within the BIOS. Otherwise you could try a CMOS reset (just ask us here or Google it if you're not sure how).

One thing with a CMOS reset, be sure to go into BIOS directly afterwards and set the correct date before going into your O/S, just in case something thinks it's expired.

does it just open BIOS and then not try to boot to the os? it could be that it isn't recognizing the Hard drive. check in your BIOS to see.

With such little info it is hard to determine what the problem is. these are just educated guesses.

try running the OS directly from the CD if it boots to the cd. i think you might have hard drive issues. another thought. check your boot sequence make sure that it is set up to boot from the floppy(if aplicable), then CD, then Hard Drive. take any floppies or cd's out of you computer. it could be trying to boot to another source.

just a few thoughts