hi, recently my screen goes to black for a few seconds and then changes from 32 bit to 8 bit, stays like that for about 15 minutes or so and then sometimes changes back again. i tried  a new video card but the same thing happened thus eliminating the question whether it was the video card so i put the same one back in. is my motherboard shot or what. thanks for your help.my video card is a

nvidia geforce 2 mx/mx 400.