If you haven't done so already you might put a copy of your post over in the Dimension - General Hardware forum.  Since your problem doesn't appear to be BIOS related you would probably get a better response in that forum.

My shoot from the hip guess would be a bad power supply since the power button is yellow. I guess it would also be possible that you have a bad power button. Post in general hardware, you'll get more help than in the bios section.