I suggest a methodical approach:
If your BIOS is not seeing your hard drive then you are not going to get anywhere so you need to find out why.
Assuming you have not disturbed its wiring or installed anything before this happened, check the ribbon cable connection to the hard drive both at the drive and mobo end. Go into BIOS (tap delete is the usual way on boot up) and ensure it is set to auto detect (although it sounds like it is). If all this is ok and your drive is still not being seen, you might have to face up to the fact that it has died.