BF3 freezing

Hi All first post here so please forgive any mistakes, hope this is in the right place. My problem is playing BF3 I can play the single player great with my 6950 and the graphics are awesome.The problem is MP I have been trying for the last day or so but every time I play MP the game freezes on me and the only way I can get back to windows is to press the button on the tower.I have uninstalled and reinstalled origin and BF3, played PB and non PB servers.The game crashes in about 5-10 mins every time.I have tried 11.9 and 11.8 drivers the longest I played today was 13 mins with 11.8. I am a more or less a noob when it comes to computers but to my way of thinking if the graphics card plays the SP great there cant be that much wrong with the card or am I missing something. any help will be appreciated but I have a feeling this is one game that's going to pass me by. My build is below
Intel Core 2 Quad Q6700 LGA775 "Kentsfield" 2.66GHz (
Asus P5Q Intel P45 (Socket 775) PCI-Express DDR2,MB
Corsair VX 550W ATX Power Supply (CMPSU-550VXUK)
Western Digital Caviar Black 500GB SATA-II 32MB Cache
Antec 300 Three Hundred Ultimate Gaming Case
Kingston HyperX 4GB (2x2GB) DDR2 8500C5 1066MHz Dual Channel

Thanks for your reply I will try and add details that I know. I have after burner to check the temps, and nothing is over clocked.

Sorry pretty new to computers UAC?

Thanks I will try with the motion blur off what was that first one?