Air condition Problem

[Katlynn]

I have a airconditioner that i bout off a friend. this is my second year with it and now it doesnt seem to run. when i turn it on to fan only i dont hear anything but when i turn it on low/med/ hi ac i hear a err type of sound. i was wondering if there was something i could do to fix this because i dont want to go out and buy another unit. HELP ME PLZZ!!