your disposal is locked up. either the motor is bad or more likely something is jammed in there and the motor cannot turn, thus the humming. kill the breaker for it, and reach in to see what you feel, you may find a fork/spook caught in it.

as to why it clogs, if the impeller is partially covering the drain side it will drain extremenly slow. any little bit can cause a further restriction and make it not drain at all. ours does this periodically when our daughter washes her plate off in the disposal side but does nto turn it on.

Many disposals have a wrench that inserts into the bottom of the unit to allow you to turn it by hand and unstick it. Open the cabinet and see if there is a wrench in a plastic sleeve on or around the disposal.

If it's not there, look at the bottom of the disposal and see if there is a hex opening in the center of the unit. You can probably get a new wrench at a hardware store.

"Any pipe/drain declogging liquid does not help at all."

You should stop putting any drain clearing chemical in the disposal.

It will damage it and shorten its life.

As mentioned above, it is jammed with something if it is humming.

Turn off the breaker and look and feel till you find the cause.

There should be a hex recess in the bottom of the unit to unjamb it.
You may be able to put a hex wrench in and rotate it back and forth to free up the disposer.

if you dont have a wrench use a broom handle from the top. There is also a little red button on the bottom to reset. Use this if the unit stops humming while trying to unjamb. How old is it? They do rust out.

You didn't say what brand/model or how old but from your description I'd wager the grinding mechanism is worn or eroded to a degree that it no longer grinds/chops as it was designed to and is passing clog-prone-sized bits down the pipe. I've serviced several disposals where the owner reported no suspicious sounds but, upon examination, it could be seen that portions of the outside grind-ring were bulged out or even burst. On other occasions, the grinding surfaces were simply worn out. I suspect that is likely what you're dealing with.

However, do get it un-jammed first.

If the unit happens to be ISE, replacement will be a breeze, although probably a little messy assuming you've got clogs in there.

When I did a search of all forums for "chueh" there were 34 threads and every one of them was started by you. That must be a record!

You should have an angle iron that came with the disposal. Insert the angle iron into the hex spot on the bottom of the disposal (underneath-inside your cabinet)

If you don't have a angle iron your handy neighbor most likely does. They are universal in size-one size fits all disposals.

PS Turn the angle iron once you have placed it into the bottom of the disposal. this will dislodge the problem.

I have a friend who has had this issue. The problem was his wife. She kept (and keeps) things on the window sill above the sink. Like her rings and spare change. And every once in a while one of these things gets depressed and takes a swan dive into the disposer. It then gets jambed between the rotating chopper and the sidewall, seizing it up to the point that the unit has to be removed and disassembled to free it up.

Don't ask me how many times this has happened.

Vegetarian issues are usually the problem. Disposals hate asparagus and potato skins. If the side with the disposal is not draining you have a clog in addition to the disposal being stuck. You need to do 2 things..use the hex key to dislodge the blades, and you need to unscrew the waste pipe the exits the disposal and hooks up with the waste line beneath the adjacent sink. That is where the offending clog will be found.

Don'cha love people who never come back? Carry on, chueh!

Happened to me recently...I used a flashlight first to see what I could see in there, and saw nothing odd, no utensils or food. However, there was the head of a large bolt or a nut at the center of the disposal "floor". Using a racheting socket wrench with an extension, I found the right socket and turned it a bit...be sure to turn it in the direction to tighten it, you don't want to loosen or remove that thing. This easily got the disposal freed up and it has worked fine since then.

In the process of fixing it, though, I did some internet research and there are lots of sites out there that tell you exactly what tends to clog up disposals and subsequently clog up drains after going through the disposal. I'd suggest taking a look there to see what not to put in your disposal for future reference.

-Roger

But the answer's still there to benefit the rest of us, asolo.

Thanks for asking, chueh!

I'd like to ask Chueh the final result because my garbage disposal has exactly the same problem as Chueh's.
I lease a house and suppose the landlord should repair it, but I met a bad one who doesn't want to send people to repair it because my rental will be end in 1.5 month. What should I do??

"I lease a house and suppose the landlord should repair it,"

If you allowed something down the disposal that jammed it the repair would be on you.