Motor hums but door will not open

see if this link helps you out.... https://www.google.co.uk/webhp?sourceid=chrome-instant&rlz=1C1CHBD_en-GBGB719GB719&ion=1&espv=2&ie=UTF-8#q=Garage+door+won't+open+but%2C+motor+hums

Could be stripped gears internally. Take cover off and look. It will be obvious.

If the motor is running and the chain or belt isn't moving, you have a broken gear in the opener.

Either the opener trolley is disengaged or you have a broken gear/sprocket assy.

If the door is not stuck in the open position and just hums you could have a bad start capacitor. It is alongside the motor and has 4 wires going to it.

Sounds like you have a bad start capacitor. It sits next to the motor and is about the diameter of a silver dollar and about 5 inches long. You can get one at any good door opener service company.

Remove the cover from the motor unit and you will find the drive gear has stripped. White sawdust all over. The part number for the gear kit is 41A2817 and it comes with instructions. It is available at any good door opener service company.

If the motor is running but the chain isn't moving you have a stripped drive gear. Remove the cover from the motor unit and check. It should be obvious.

My neighbor guy, who knows a lot about stuff, told me to get a new one.
Good solution.

I just had the same problem. Extreme cold, garage door stops working, motor hums, same here. I opened up the my garage door opener(after unplugging it), and found that the wormwheel had a wear spot on it. This is the gear that allows the motor to raise and lower the garage door. Any way, after the wife "sugested" that the door was too heavy to lift, I went and bought a new garage door lifter. But if you are handy dandy with tools, I have seen the wormwheel for sale here. http://www.aaaremotes.com/gearsprocask.html It's the plastic wheel that went bad on me. If I would have found this before buying the garage door opener, I would have got the sprocket assembly. I hope this helps!