SOmetimes when i play 5 min and sometimes i can play hours but Game freezes my PC and only thing i can hear is stupid sound, and i cant do nothing, only restarting my PC on buton on computer.
My pc configuration:

Dual core processor
1 GB video card
Win 7 64bit

P.S. this started to happening few weeks ago, and working fine before that , i had 512 video card so i boughted 1 GB because i thought it was problem with that, 2 days ago i updated bios and drivers because i thoughted it was problem with that, but all of that camed without resaults, so please if u know what could it be . thanks