i cant afford a good cpu cooler and a gtx 670 to oc my cpu. So i am going to let it on 3.9 stock. If i go for the gtx 670 what psu needed for that card ? i have a 650w
A 650 Watt is fine, just make sure that it is a reliable brand such as Corsair, Antec, Seasonic, OCZ,etc. If you cant afford a CPU cooler than no problem. I am just telling you not to expect Ultra settings on BF3 (VERY CPU heavy game). Other games should run fine.