lcd monitor or graphics card problem

i have the following sys:
intel c2d e6700
asus commando mother board
2*2gb transcend 800mhz ram
250gb sata 2 hard disk
vg1930 viewsonic 19inch lcd screen
leadtek 8800gts 640mb
windows xp x64
my problem is that I get lot of vertical lines on the screen a startup and i am not able to boot into normal mode, but i can get in safe mode. at first i was able to go into normal mode but after few seconds part of the screen was getting filled by violet color and the system gets stuck and i had to restart it....i changed the graphics card from the currnt pcie slot to another which i havent used before but the same problem occured. i even chnged the monitor interface from dvi to d-sub still no change, at first when i used d-sub the whole screen became violet instead of part of the screen. later wen i removed the d-sub cabal and reattached it, it became normal but still aprt violet appeared and system got hanged.....after some time i could not boot into normal mode, but was able to go into safe mode....i have the latest nvidia graphics drivers installed....the problem didnt occur immediately after installing latest drivers....wat is the problem my monitor or graphics card???