When I had that issue, GPU shutting down the computer with the GTX550Ti, it drove me nuts. I tried everything.
I finally removed that Video card and replaced it with the GTX 460 that was running in my office at home.
That problem came to an end.
I since have tried it in other computers for folding and none succeeded. Funny thing that it works fine if I am not folding, or stressing it, but a no go for folding.
I since have removed my spare office computer and brought it home and have it folding away in the corner of the family room at other side of the house from our bedroom.
I bought a TP Link model TL-WN722N high gain network adapter(wireless) to work with the TP Link BGN wireless router at the other end of the house.
It could not work any better!!!!
Bottom line.
Sun, cards do wear out and go bad. That happened to mine.
I have yet to replace it. I have several other "WANTS" on my short list, such as that Lenovo laptop
G580 from microcenter.com, some additional 12 ga.2 3/4 in., #0 buckshot shells, and we want to have a window removed and bricked up outside with matching brick that we have, and obviously insulated inside wall and finished with drywall and painted.
This allows us to redecorate the master bedroom.
We also need at the same time the siding uner the gable ends replaced and all trim around the house and new soffits installed so the attic can ventilate properly.
So we have a little on our plate yet.
I think you should consider TRADING VIDEO CARDS from a known good one to your computer that is giving you trouble.
If you still have same problem, then it is not your video card, it is computer related.
Likely power.
Just a few ideas for you.
micro 
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