Check out my thread on the same problem:
http://forum.1cpublishing.eu/showthread.php?t=2338
My Asus GeForce EN7900GT TOP/256MB RAM crapped out after a year and a half. Fortunately though the card's warranty was still active, so I returned it to my computer shop for an RMA to Asus. I'm still waiting to get it back. In the meantime I bought a used ATI Sapphire X1550 card for $86, which works flawlessly with DTS and all my other games and DVDs.
Do you have graphics problems with other games/programs?
Is your cooling system in your computer sufficient?
If the answers are yes then you should consider RMAing your card or better yet acquire a newer and better one (if you have the means) as your card is quite old.