Hi Louseb,
I hate to hear you are having issues. Did you just upgrade to 10.7.5? This can cause permissions issues, and permissions would need to be checked for accuracy in the root directory. This can also be the cause as this version of the OS is not currently available from the driver downloads listed for this unit. Click Here for available drivers based on operating system. This could also be caused by a defective USB port on the printer. Test the printer with another computer to see if the device is detected to determine if the port has malfunctioned.
Hope this helps!