Connect your PS3 controller to your console with a USB cable and press the PS button to sync. If your PS3 controller won't sync, try resetting it with a paperclip inserted into the reset button hole.
I have a variety of issues relating to USB. At first I thought it was just my PS3 controller and the bluetooth dongle, but then I found out I can't even use another non-PS3 gamepad that uses RF with ...