10 times BSOD while playing Assassin's Creed or browser games

Hi all, I experience for quite a while BSODs (10 so far) when playing Assassin's Creed Revelations or a browser game. I can sometimes play it for hours but often it just crashes after 5 minutes, giving me errors like Unknown DRIVER_IRQL_NOT_LESS_OR_EQUAL (http://www.google.com/search?q=Unknown+DRIVER_IRQL_NOT_LESS_OR_EQUAL) or PAGE_FAULT_IN_NONPAGED_AREA...