The motor tries to start with a low hum, but it will not power up. The blades turn easily and the reset button is not out.

If blades rotate freely, then there is no stoppage.
If motor hums, then circuit and switch are good.
If motor will not start, and reset is not tripped, then disposal has gone bad.

Motors slow down and overheat, and then they stop working.
Each time you hear motor humming instead of rotating, the motor is overheating.
All motors stop working some time.

There are no repair parts for disposals.
Drain is not clogged, so sink is usable until disposal is replaced.

I wrote EZ disposal-replacement steps from years when I worked apartment maintenance.
http://www.fixya.com/support/r7929008-replace_garbage_disposal

Also take advantage of fixya phone service.
For a price, expert speaks with you over phone while you work on disposal or any do-it-yourself project.
Fixya is always less expensive than a service call.