Formatting probably won't change antyhing, since you're getting an error at post you know it's a hardware problem, not software. Heres somethings that it could be:
Your old IDE Cable (80-pin) died partially, but still enough for your computer to realize the HD was connected and attempt to boot. And you replaced it with a 40-pin cable.
A pin got bent or broken on the hard drive's IDE connector and not all pins are connecting.
The cable thats connected is a 40-pin ide cable and the hard drive is set to use 80-pin in the bios (probably something asking weather the hard drive is ata66, 100, or 133)
Or the hard drive ide controller somehow got fried.
Easiest solution, see if you plugged an 80-pin cable in ( literally if theres 80 tiny wires on the ide cable) and if not, set the hard drive to ata66(or 100 i forget). Or buy an 80-pin cable. Keep us posted! and good luck!
