http://www.chamberlain.com/doityourself/pdfdocs/114A3282.pdf
Please find your user manual above, for reference..
Most likely you have had a controller or drive failure? either that or a sensor has failed?, one simply must troubleshoot each section to tell. It is impossible to diagnose without actually testing the unit.
You need to see if there is drive to the motor, as it hums i suspect there is? but obviously something is preventing it from working, only a loss of drive or command to do so can cause this. It maybe the Microprocessor not "Telling" the motor to operate F/R. But it also may be a sensor preventing it from working, accordingly check all sensors. Also the motor too, as even though it "hums' it still maybe faulty, perhaps a shorted winding etc, testing the motor with a meter will tell you if it is faulty or not, the motor should have a lowish, resistance reading across the terminals, remove power first, to measure.
If you wish to DIY, then first one must obtain a service manual, I have searched but have been unable to locate one? Using said manual one then must perform the troubleshooting steps to locate and isolate the faulty component, with a view to replacement, and using the same manual glean the parts numbers and purchase the components.
It may indeed be better to call in a professional to at least first only give you a "Quote" as to whats wrong and potential costings? At least then one is appraised of things and one can then "go from there" as to what to do, repair or replace?
