I am a new home owner and when i bought the house I had a new garbage disposal installed. This was about three months ago. It worked perfectly until about two days ago. Now when I flip the switch I hear a humming, but the blades don't move....no grinding. Doea anyone know how to fix it?

depending on the brand it is some have a place underneath for a large allen wrench other types must be done from the top.
most likely it's just stuck and needs to be freed manually by rotating it forward or backward whichever works.
look down into it also with a flashlight and check for something stuck in it like a coin or something.
unplugg it or turn off the power before you put your hand down there.

Some require an Allen wrench to unjam them and others have a manual reset button located on the bottom of the unit.

DO NOT place your hand inside if the power is not disconnected

forgot to mention the reset button. but if it's humming like you said,chances are the reset hasn't popped out.