Well, your pc is spec'ed well enough, did you install the newest drivers? if so, try reinstalling. or you could just have gotten a slightly bad card, ive had bad cards before
It's probably software - bad cards tend to exhibit problems All the time - corruption on the desktop and in games, or crashing as soon as a level is loaded.
Hunting down offending software is a pain, though - I hate when something like this happens. DL GPU-Z or Afterburner so you can monitor your video card during games, CPU-Z so you can make sure your memory and CPU look good, and HW monitor to check for temperature/power issues. Task manager, too - CPU load and keep an eye on processes that consume a ton of memory/CPU time.