I'm a little unsure what to suggest on this one, it does not sound like a problem with the game. No one else has reported anything like this and you said it previously worked fine on that system.
You could try looking at your DXDiag log file or send it to us to take a quick look, it might point us to some clues. Also consider if you've made any software changes since the last time you played. This sounds more software related than hardware related.
To get your DXDiag log file;
1) Go to the Start Menu, pick "Run...", and type in: dxdiag
2) When the dxdiag program comes up, pick "Save Information", and it will save off an info file to your drive.
3) Send the info file to: firstname.lastname@example.org
4) please include the following text;viewtopic.php?f=26&t=14583