New computer unstable

Hello, i have just purchased a new computer. I have made a few comps in the pas and never had any real problems but this one is making me crazy.

Here is what i have got (just encase i have done some silly error here)
AMD Phenum 2 x3 720 black edition
GByte MA785GMT-UD2H
4GB Corsair TwinX XMS3, DDR3 PC3-10666 (1333) 240 Pin, Non-ECC Unbuffered, CAS 9-9-9-24
800W PSU ( all the connection i need)
500GB WD HDD
ATI 4770 HD graphics card

I can not seem to work out what is going wring with this computer. I installed Vista, this went extremely slowly for some reason. Once this was done it crashed when it tried to work out my computers "Windows Experience Index". After this i rebooted and it loaded windows fine, for about 10min. As of then the computer will crash/freeze randomly some times it will be fine and i was able to get the drivers on (only after a few hours of persistence). But i keep freezing some times not even making it to the loging screen. Do you have any idea what this could be. I have checked the connections in the computer but i might have made a mistake.