NVIDIA Driver errors

I hope someone can help me - I'm at a loss as to what to do next.

I've recently had a local computer store (MicroCenter) build a computer from parts I ordered. The tech who built it said that, during installation, the memory caused some problems when trying to load Windows 7. He did a memory test and said it turned out fine. I took the computer home, and within 24 hours I saw a recurring problem:

Randomly, as far as I can tell, the screen will go black for anywhere from 1-15 seconds. When it returns, I see this message:

"Display driver NVIDIA Windows Kernel Mode Driver, Version xxx stopped responding and has successfully recovered."

I've gotten it for driver 295.73 and for 3035.6. I took the computer back to MicroCenter and the same tech who built it. He ran multiple memory tests and a VGA stress test. He said there were no apparent problems that he could replicate, so he downloaded all new drivers. I just got the computer back today, and guess what happened within 2 hours of powering up?

"Display driver NVIDIA Windows Kernel Mode Driver, Version 295.73 stopped responding and has successfully recovered."

I'm at a loss. Why would a tech be unable to replicate the error in 4 days, yet I get it within 2 hours of being told it was fine? It cant be the configuration - no change from when it was at the store. Here are my specs:

CPU - Intel 3930
Motherboard - ASUS P9X79 Deluxe
RAM - G Skill RipJaws DDR3 1600 32GB (8x4)
GPU - EVGA GeForce 570 with 2.56 GB

Can anyone help?