This had driven me crazy for a long time, until I stumbled upon this page from Microsoft
. It turns out that it's the useless E-Support button on the front of your 8100. I popped open the case to see if there was something I could unplug, but it looks like it's connected through the same cable as the power button.
You can either install the driver for it (most likely on the drivers CD that came with your Dell) or try to cut some of the wires (risky) to disable it.
Hope that info helps.