pc freezing alot

hi guys a few days when i was playing a game called aion i noticed the game froze for a few seconds i thought maybe it was due to the server or something thne i found when that pause happen the music am playing in windows media player also stops and later the whole pc just freezes in any game or when browsing the fire fox get not responding just a freaking freeze i tried the memtest program one i had to install on a usb and booted from it and it passed with 0 errors so i guess its not a ram problem ? i installed a virgin copy of windows and still the same trouble (windows 7 64 bit) this is really driving me crazy the pc is around 6 or 7 months old its been running perfectly for those few months i dont think i have downloaded any upgrade to the driver or the hardware before this happened i can still move the cursor other than that its a complete hang for a few seconds and the program has stopped responding shows alot now lol my buildis amd phenom II x4 965,msi870-g45,cooler master 650watt,4gb ddr3 1600,windows 7 64 bit, i even tried safe mode with networking still the same thing couldn the games though ....thanks for your time