Are all your BIOS settings stock? If not, clear CMOS, test games, if everything is good, change desired settings in BIOS one at a time, and test game after each change. Tedious, yes, but worth it in the long run.
Perhaps Memtest your ram, and if that doesn´t do it, clear CMOS, flash latest BIOS, or if it´s the latest version, try older BIOS revision.