XFX 7950 Shutting down pc

I recently bought a xfx 7950, as soon as i received it I installed it and powered it by using 1x6pin and i put a 6pin to 8pin adapter on my other 6 pin, after enabling eyefinity I ran furmark to test the performance but as soon as I hit burn in test the pc completely shut down. Another time I launched far cry 3 and as soon as I got into the game I played for about 5-10 seconds and it turned my pc off again, I have read a few articles and some people say it could be the psu, I have a cheap psu could this be the problem, the psu i use is this http://www.scan.co.uk/products/750w-alpine-alpine-750w-... . Any help would be much appreciated.
Rest of my specs if you need it,
Phenom x4 @ 3.3 GHz
8gb g skill Ram 1333
gigabyte motherboard with pci e 2.0 (sorry dont know exact model)
24inch acer monitor using hdmi
21.5 inch acer monitor using dvi