GPU crashes running Benchmarks or Games

[XKGhost]

I decided to replace my Sapphire HD 5850, opting for a Gigabyte GTX 660 Ti OC. Once the new card is installed, desktop works perfectly, but if tested with Benchmarks, the GPU crashes. By starting FurMark, the card crashes to the lowest 400x300 resolution, this is where the black screen occurs and I have to perform a hard reset to restart.
I do not think this is a temperature problem, since neither the CPU nor the GPU have time to overheat. The only temporary solution I found was to downclock the card to the minimum. At that point it works with few FPSs and bad performance, but it works.

The card should be perfectly compatible with my hardware, even if the motherboard is dated.

Reading on the internet, many attribute this type of error to a damaged PSU, but before replacing it I would like to make sure that is the problem.
I just formatted and reinstalled Windows 10 Pro with the latest nVidia drivers available (3.84) so ​​I do not think it's a software error.

My specifications:

Mobo: Asus P5N-D
RAM: Corsair XMS2 DDR2 800MHz (4x2GB)
CPU: Intel Core 2 Quad Q9400
GPU: Gigabyte GTX 660 Ti OC
PSU: LC-POWER Power Power LC6600GP V2.3 600W
HDD: Western Digital WD Green WD10EARX 1TB

 

[kookie3010]

usually this point to the psu.if u can try ur card on a friend system to cancelled out that the card is faulty.

 

[XKGhost]

i can't try it, but the card is stable when is downclocked. Do you think that it could be faulty?

 

[kookie3010]

i can't try it, but the card is stable when is downclocked. Do you think that it could be faulty?

only way to find out is to use another power supply or a different card with the same power draw as the 660ti.