Computer freezes when playing!

Hello!
 
When i start playing, my computer often freeze and i have to reboot to fix it. When it happens i can move for a few seconds after the game has loaded and then the video freezes and shortly after all the sound stops aswell. I´ve tried everything once the game freezes but rebooting is the only solution there. 
I´ve read a few threads here which said changing "anti-alias" and "Vsync" can fix it but that did not seem to do it for me, it worked for one game but the next time i played it was back to normal but that don´t work anymore.
I don´t have Nvidia, read that it might cause problems with the game.
I had the same problem in the first game but that was caused by looking at the lava (or that was a coincidence everytime) but in Orcs must die! 2 it freezes at any time.
I purchased all the dlc recently and i don´t remember any crashes before that but i hadn´t played in a while before buying the dlc, perhaps its the dlc who causes it.
I appreciate any help, every minute i can´t play is a minute i´m not slaying orcs!