just a few things you pry already thought of...
1) Open up your box, check to see if the IDE cable is loose.
2) Pop your HD into the freezer for 30mins. Let it sit for a bit. Make sure no moisture is on it. Pop it back in. (yes it works, power surge hit my whole city, fried my drives. put them both in the freezer, and BAM! work again).
3) Pop the HD into another box to make sure its not just your computer (possibly a mobo issue [uh, thats mother board])