Ah, I see. Sorry, it didn't click about the demo version.
Can you post your dxdiag, please?
Here is how to do that:
Click Start button. Select "Run". Type "dxdiag" and press "Enter".
(If using Vista you may have to press the Windows Key + R to get the "Run" prompt, depending on how your system is set up)
You might be asked about WHQL drivers, click "Ok".
In the next window click the button that says "Save All Information", when the Save Dialog box appears, save the file to your desktop.
To upload the file here, select "Reply" to this message. Select "Additional Options" (underneath the text area) and choose "Browse". Browse to your desktop, click the file and click "Open". When finished post the message