Harddrive Disappeared.

My brother was playing Skyrim, the other day. He hit a loading screen in game and it sat there for a while longer than it should have, then it just randomly closed with no notification or error message. He went to reopen it, and windows popped up with it's default "Windows can't find this drive if it's a network drive check or connection" or something to that extent. (It is not a network drive)

Opened Windows Explorer and that hard drive was not listed, Also checked in Device manager, Disk Management in MMC, and Open Hardware Manager, it wasn't listed there either.
Restarted the computer and it showed up, opened up Skyrim and it ran with no problems, along with some other programs on that same hard drive with no problems.
The next day downloaded a game from Steam, onto the same hard drive, and after maybe ten minutes the game freezes and closed, Steam prompted that executable was missing upon trying to reopen the game. Opened Windows Explorer and the hard drive was gone again, restarted the computer and it came back.

System Spec-
http://pcpartpicker.com/list/WBHqkT
It was the Seagate Barracuda 500GB 3.5" 7200RPM internal harddrive

Any help appreciated.
Spock96