RAM is underclocked need help

im running 2 sticks(2x2 gigs) of ddr3 memory that is rated at 1600 problem being it says in my bios that its running at 1333 my mother board supports it (1600) and i tried to get it to stock clock but when i changed my settings and set it to 1600 when ever i would run a game (L4D2) it would crash along with other games and by crash i mean it would restart my whole pc im not sure on the details i should post here for further assistance with my problem so if there are any questions i will happily reply with what ever system specs you ask for thank you in advance for any tips or advice