Could you please supply your system specifications or dxdiag, this may help us to determine the problem.
Your dxdiag can be obtained by following these instructions:
Click Start > Run. type in dxdiag and press Enter. You may see a popup asking about WHQL drivers, click Yes/Ok to proceed.
In the window that appears, 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, click Additional Options underneath the reply area and choose Browse near Attach. Browse to your desktop, click the file and click Open.
* Windows Vista users need to press the Windows Key + R to access the Run prompt.
You can then post your reply with the file attached.
This might help us to see what the problem is.