Dell Precision 690 - Problem with Power On Button

Hi

Over the last week or so the power on button on my Dell Precision 690 is starting to get more difficult to press.  Today I cannot power on PC as it has become completely jammed.  It looks like I am going to have to remove it.  Does anybody know exactly how to do this as its not in any of the users documentation.

Would really appreciate any help as I need to get PC back up and running.

Thanks