Look for a CMOS/BIOS reset jumper. Many dells have them and the model is missing so I'll only add that we usually can slip in some USB PCI card to stand in.
I got a new tablet for Christmas, and I plugged it into a USB port on my Dell desktop. The tablet showed charging but would not power on. I unplugged the tablet from the USB and suddenly neither my mouse nor my keyboard would work. All USB ports seem to be completely dead. Because I have no way to hook up an input device (there's no PS2 port), I can't get to settings.
I tried powering off and unplugging the desktop for about five minutes and then powering back on. I've tried powering on/off with the keyboard plugged into any or all USB ports, and the keyboard does not light up, not even before Windows starts up.
Any suggestions? I've already had several people tell me to go to device manager, but remember I have no input whatsoever.