OK, this pretty clearly sounds like a problem relating to the IDE chain. Ah, but what?
Without laying hands on the system, my gut reaction is failing hard drive, and hey, it happens all the time (we just had a discussion about this over in the Hardware and Software forum). My Gut Reaction here is that the failing hard drive, while Slave, was sending spurrious signals to the mainboard regarding ALL the hard drives on that chain. The BIOS, unable to figure out the status and existance of bootable hard drives, threw up that error message.
Now, if I COULD lay hands on it, I would start moving that drive around and see what happened. Take off the CD Rom drives, put that "bad" drive on the secondary IDE chain and make it the drive "primary" or "single." Set the BIOS to auto-detect the drives. reboot.
Then look in the BIOS again. Are the devices on the secondary chain "unknown" or "unrecognised?" Bingo! That drive is the problem.
Maybe the IDE controller chips on the mainboard are failing. This is rare, but I;ve seen it. Adding a PCI IDE card (I like products from the comany "Promise") solved the problem.
Anyway, start shifting that drive around (even installing it in other computers) and see if the problems follow it.
-Llama