Taking the proper precautions, I took apart my old Dell XPS R400 to clean. The oh so conveniently placed HD bay blocked the vents on the front of the case and a lot of dust had accumulated in the space between. In removing the module that held both the Floppy & HD I found that the ribbon cable (not individual wire connectors) that connects to the front panel pins on the MoBo was bent double at the connection to fit in the tight space. When I tried to boot up - no power was getting to the MoBo. My guess is that the powerbutton wire(s) fractured during cleaning and I need a new cable. I don't have the MoBo documentation or color coding on the front panel pins so I'm a little nervous about taking a screwdriver to what I believe to be the power-on pins to test my theory. I tested the powercord and it's OK, I don't have a spare powersupply yet to test that - the computer is 6+ yo and everything but the HD is original.