Hi, 

Something must be disconnected in the front bezel causing the power button not to respond. The button that you are using to turn on the system is for the purpose of testing the power supply (like when there is a no power issue). If you press it and hold it, it’s supposed to power up the system. We recommend removing the front bezel to make sure all of the cables are properly connected. You can refer to the Owner’s Manual for removing the front bezel (page 129).

This has been a problem with the power button sine the R1.

The chrome button is on top of the actual power button. The Chrome button plunges down onto the power button underneath. Try to use two fingers on either side of the Chrome button and push down evenly.

When I was under warranty I called about this and they sent someone out to replace the front bezel. The front bezel is not the problem. It is a separate switch and I was never able to get Dell to fix it. I finally gave up.

Had the same problem with my R4 I bought in 2012.  Brand new, the power button was not working correctly.

Unlike you, I gave up before calling Dell, I knew it woulb be more problem trying to repair the button than endure lol

Well, the button work each time, I just need to press hard.  But most of the time, the computer stay on.