If you're stuck from startup, try hooking up a USB keyboard and navigating to menu->controller settings->configure a controller. Then you may be able to push a button on your gamepad, initializing the configuration process. While you're in this screen, you can also try cycling through your inputs for "Input p1" to see what appears. If nothing is there other than "default", then the pads really aren't getting detected.
Also wired or wireless? If wireless, try checking to see if the wireless dongle actually works by testing it on your PC or another system. Try connecting using different USB ports on your system also, as sometimes these can go bad.
These are basic suggestions, so apologies if you've already tried this stuff. Without more details though, no one can really know what you have or haven't tried.
