nvidea 6200ge blownup grapics

I have buid a new pc with a asus n6200ge grapics card
now sometimes even when going nothing i get a blownup display on my monitor
evereything els is working but the picture i get is blown up
Sometimes it happens when i'm in a game so i use the button on my mouse to
go back to a difenent open window and its back to normal
sometimes it happens a few times in a day and other days not at all
i have try's with different drivers even some new betadrivers and the old
one from the install cd
but i get the same problem after a while
even plugged my tft on the dvi port nothing changed
I'm glad i have the extra button on my mouse to swith windows
my old system was whit a nvidea 5700 in it no problems at all
i dont have the 5700 anymore to i cant test my system with another grapics
card
evereything in this pc is new mb-chipset-cpu-grapics card

Is there somebody else whit the same problem who can help me so i can fix
this