Interesting, are you working with ProTools? I am a music and audio geek myself :-)
With regards to the graphic card, I guess you are right. Based on your description, It is highly unlikely this would have caused the error. The issue could therefore be narrowed down to either a faulty memory module(slot), processor(socket) or in the worst case, the system board.
Anyway, I assume that your new Z840 will operate flawlessly.
