Disconnect usb and try again. Still no justice, reboot. Still nothing? disconnect cable from computer, turn phone off, connect USB then power up your phone. Hope this helps.
I went to USB debugging (Menu-->Applications-->Developement) and checked USB Debugging and turned off the USB debugging notify. Then my started to work. Sometimes I have to plug, unplug and the plug back in to the computer for it to work. In the steps in figuring this out I may have turned dubugging on and off like the poster above mentioned.