Last weekend, I reinstalled Windows 7 Professional x64. Since then, I have been having BSODs that reference ntfs.sys, System_Service_Exception, and Irql_not_less_or_equal. These occur when I attempt to play games (especially Mass Effect 2 and Dragon Age - the average time between game start and crash is five minutes). Memtest turned up nothing after 7 passes. Any ideas as to what could be causing this?