hi you may have a loose grafix card! check your conection at back of pc, if this is ok! check that the card is seated ok in the slot in the pc!
if the pc keeps closing down! it may be that you have a slow fan full of dust! and componants in the pc are getting warm! this will cause the pc to crash! or stop!
if none of above I surjest you re-install windows.
good luck.
dangerous752
March 2009