Avid Pro Audio Community - 'Unable to locate M-Audio hardware. Make sure your hardware is connected and turned o

: When I launch Pro Tools MP9 (M-Audio Fast Track C600) I receive an error message indicating 'Unable to locate M-Audio hardware. Make sure your hardware is connected and turned on'. Click “OK” when the hardware is ready.
I’ve been using pro tools for a year now without a problem. I unhooked it recently and took it to a friends house where it worked fine. I brought it back home and that’s when I started having this issue. My M-Audio device is connected and turned on. I’ve tried all the USB ports I’ve opened up the computer to make sure something didn’t come loose. My keyboard is plugged into the M-Audio box and I do get sound from the speakers. I’ve been to this web page http://howtoprotools.wordpress.com/2009/08/07/unable-to-locate-digidesign-hardware/ and checked the drivers in the device manager. Everything looks fine there. I even tried to reinstall the drivers. Why won't Pro Tools launch?