[leodlion]

The two previous posters may be right, you dont have the right disc driver. Make a note of the HD maker and model and try to get a free driver from the internet. Or see if you can locate the installation disc of the HD and install the driver from there.

The other thing I would do is make sure its really the HD thats causing the problem. You tried swapping difference things e.g. ram, power supply, etc. Is there a way you can put back the old working HD and yank out the one in there now? If the PC works, then it must be the HD. If not, you got some other problem.

I just noticed from your post that the HD has XP on it. And you booted from this HD? If this is true, then try reformatting the HD if you dont need any data from it. Otherwise, you need it backup but now its gonna be a pain because you have to find another cpu to plug the HD on.

Good luck.