I have a Windows XP system that was working but I opened the box to replace a graphics card fan that had died. When I put it back together, it wouldn't boot. I took the hard drive out of the box and connected it to another system as a second drive and was able to read it fine. I put another bootable drive in the original box and was able to boot it.
So, I put the original drive back in the original box and did some testing. I found that if i remove the IDE interface cable from the hard drive, the drive will spin up. I can feel it if I hold it in my hand. As soon as I connect the interface cable and try to boot it, the hard drive refuses to spin up. I put the other bootable drive back on the original box and now it won't spin up at power up time except for one time out of maybe 5-7 tries it booted OK.
I have replaced the interface cable but that doesn't seem to make any difference. My guess is that something is wrong with the mother board that is intermittent. The box was FULL of dust when I opened it so maybe in cleaning it out I have upset some delicate balance of fuzz on the circuitry. :-)
Anybody have any ideas how to troubleshoot this box or what might be causing such odd behavior.