Try connecting it to the other socket on your motherboard. Also if an IDE/UDMA/PATA drive double check the jumper setting. Made any changes to the system before this happened? Noticed any clicking or other "new" noises from the drive on bootup? I'm assuming the cable is keyed so it can't be installed backwards, never seen an 80-wire cable that wasn't like this.
Last resort, try a different cable (unlikely but they do fail), if no joy try to install as slave in another PC and see if it shows up in the BIOS there. If it does download and run the mfr's diagnostic utility.
I'm not gonna lie to you, it doesn't sound good. Basically when a HDD is not seen by the BIOS it's one of those four things: bad cable/connection, wrong jumper setting, bad controller circuit on the mobo, or failed drive. Unfortunately the last is the most common.
[Edit] Sorry I forgot one -- the power connector. Check voltages w/VOM or just try a different one, most machines have extras.
Edited by DaveM59, 14 May 2006 - 04:13 PM.