Strange PC problem

Okey, so in January I bought a new computer and had million of problems by buying the parts separately. I dont want to whine and mention those annoying things so I just write down my actual one:

On Windows 7 (ultimate, 64-bit) a strange video card driver error comes up and the most annoying thing, its total random. My screen turns off, then if I'm at desktop, comes back to normal in 3 secons (if I were in a game, sometimes its coming back but most of the time I have to force shutdown as its freezes like ice). When I'm at desktop the error message is: "Display driver NVIDIA Windows Kernel Mode Driver, Version 280.26 stopped responding and has successfully recovered." I tried like 9 driver and always installed/deleted with care (safe mode, driver cleaner, bla bla). Some people say its a win7 error and there is no solution but since it makes me sometimes force shutdown, i would really need one.

My specs:

Gigabyte Z68AP-D3
Intel Core i5-2500k
Corsair TX650 psu
4*2 GB Geil 1333 ddr3 ram
Zotac GTX 480
2 normal sata drives.

additional info: no overclocking was made, even tried to disable turbo mode on my ram and my cpu but same error comes up. for me looks like a driver or win7 error so i would say its all about software but in the worst case it can be my gtx 480. hopefully not faulty.

I made several memory tests with memory86 etc, does not look like mem or video card overheating problem. monitoring my temps with aida on my g15 panel, looks normal (had overheat problem but thats totally different, my video card slows down itself and slowly i have to turn of pc else its freezing. its only happened 2 times but only after 12 hours of use. so the kernel problem is surely not about internal heat.)

Thanks in advance!