Fans spin at max and blank screen with new GPU

[Remco32]

I bought a HD6950 to replace my HD5770 card. For that I needed a new PSU, I got a 550W Enermax. With the HD6950 in the system, all of the fans in the computer go spin at max and the screen goes blank during the boot of Windows or when the computer is turned on for a while in the BIOS. The whole system functions perfectly with the old HD5770 in it.
What is causing this and how do I fix thsis?
I already tried the resetting the CMOS. It isn't the HDD, since it's brand new, and every other component works just fine with the HD5770.
The HD6950 has just been RMAd and mailed back to me, and there was nothing wrong with it according to them.

 

[Remco32]

Can it be the PSU? Since that and the GPU are the only thing that would act differently with a more demanding GPU?
Some more specs:
Q8300
4GB of RAM
Not sure of my MoBo, since the PC is a prebuild I've been updating.

 

[Remco32]

Bumping. Planning on getting a new PSU tomorrow.