If you go to the device manager, click on anything at all, then at top action | scan for hardware changes, does it make the drive show up again in explorer (Computer.)
I know it's not THE fix for this, but I had an old cheapo 20 GB EIDE drive this exact thing was happening to. Disappearing in 7 (others not tested) even while copying from it to another drive or network drive. So instead of fussing with it or trying to repair with any tools, I just canned it.
Hopefully your 1TB behaves better for you though after doing what monza and Captain Zero are saying. Perhaps there is a firmware update or something, if not? I never did that to a HDD, so I dunno. Good luck!