I have a 1TB Western Digital Sata HDD that I use as a storage drive. I have a 500GB system drive, also by WD. They are from the same family of drives, but only the 1TB drive exhibits this problem.

What the 1TB does is it drops off my drive list in Windows 7. I can't actually tell if its powering down or not; I can't distinguish between all the vibrations in the computer. The drive is also really loud when seeking, but Western Digital told me this was 'normal.'

I tried running WD's Diagnostic Software. Twice, with the full scan. And the report came back with no problems. I also called Western Digital, and the rep said if the Diagnostics came back fine, then the drive isn't the drive isn't the problem.

I'm prepared to purchase another drive and get my backing up over with, but before I do that, what else could it be? Everything else seems to run fine. I guess it might be the motherboard or the PSU, but i'm inclined to say it's the drive itself based on some other Newegg customer reviews which describe similar symptoms.