If the disposal is full of stuff; make sure you unplug it from the outlet, or turn the on/off switch to off.

remove everything that is in the disposal (including the water you can reach.  Don't put it in the sink - put it someplace else.

then; turn the on/off button on and see if the disposal motor runs.  If it does, run clean water into the sink and let it run for awhile.

Whatever you do, dispose of the dirty water someplace other than in the disposal.

If the motor doesn't run; access the disposal unit under the sink.  There should be a red button someplace on the bottom of the unit.  Find that and push it.  Keep the area under the disposal free of objects for a while. 

Now, get up and try turning the disposal on again.  If the motor still doesn't run, find the hex-wrench that came with the disposal.  You will probably need to put your head under the disposal with a light source.  Look in the middle of the disposal, place one end of the hex wrench in the middle where the disposal has a place where the wrench fits right in, and turn the wrench until you feel something move.

Now get up and try the on/off button again.If the motor works turn the hot water on and run the motor for severa minutes to see if the clogged drain clears.

If those steps don't work: call a: your landlord

                                                b: a plumber

or get under the disposal again and write down everthing you can read; and go to someplace like Home Depot where someone might be able to give you other ideas.

Good Luck!