If it cannot be seen in the lower part of Disk Manager, the one that shows each drive as a bar, then the problem is not limited to corruption. It would show, at worst, as either an uninitialized drive, an unpartitioned drive, or a RAW partition. But if you don't see a bar for it at all, it's another problem. I was going to paste a picture, but my office has blocked photobucket. Look at step 5 of this:
http://www.tomshardware.com/forum/message.php?config=tomshardwareus.inc&cat=32&post=265764&numreponse=1838027&page=1&p=1&subcat=203&sondage=0&owntopic=0#formulaire , and look at the "stripes" that I described.
If it's there, then we look at corruption. If it's not, we look at your drive, your power supply, the case, and the cable as you suggested in the first place.
Does the drive get seen in another port or on another computer?
If you have another drive, even a USB thumb drive, can it be seen in that same port?