geoff5093 said:
Refer to your motherboard manual to where the jumper is located and how to clear CMOS with it. Generally there near the SATA connectors (if you have them).
I think he's talking about the hard drive jumpers. They're on the back of the hard drive, near the power and IDE cables. Just pull the jumper off and put it back in the correct position, which should be printed on the top of the drive.
It's also possible that the boot order has simply been changed in the BIOS, if you've changed settings in there. You may need to reset the boot order so that the hard drive boots first.
Of course, you should also make sure that the cables are firmly seated in the drives.