Could also be that the C: drive died, which is why the BIOS cant find it.
Double check power and data cords to the hard drive.
if BIOS doesn't see a hard drive installed, (if you cannot select the hard drive to boot from) the circuit board for the HDD is fried. If you have more than one hard drive, make sure you can select the same number as you have installed.
If Bios sees the HDD but still asks for boot, the drive was likely corrupted and can usually be fixed by OS repair.