Hi Andreas.
To determine the problem, we need to know a little bit more about your machine. Can you please post your dxdiag, so we can help you further.
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.