Make sure the fuse or A/C breaker is intact. Be sure your temperature control is turned down LOW enough to activate the A/C. Test for current to the switch.
Check and see if your fans are running. Have your freon levels checked. This needs to be done by a qualified person. Also see if you engine is overheating. This can effect your air conditioning.
Check fuses for AC. If blown out replace it. Check temperature control. Check the AC green light. Then check the compressor. If AC clutch works therefore there's little or no freon gas. Causes of no freon are leak, old age. If AC clutch doesn't work bring to a shop.
Do you know what exactly caused the AC to stop working? In order to help you answer the question I also need to know the model year of the year and where did you buy it? This data will be important for me to answer you with the best possible response.
This personally happened to me on one of my vehicles so you are probably going to have to replace your whole cooling unit. You will need to talk to your nearest auto body mechanic.