The first step would we to check that the furnace is working as expected. To test this, you are advised to lower the thermostat setting so as to kick in AC repair mode . Your air conditioners furnace fan should start working immediately and if doesnt, it means your thermostat has a problem. You could either try to reset the circuit breaker and if this proves futile, your best bet would be to call an air conditioner contractor. Do not attempt to dismantle any part of the thermostat in order to fix it. The best you can do at this point is to reset the circuit breaker and if that doesnt work, you must call a professional.
Other parts of your air conditioner that could cause problems are the contactor and the capacitor. This two could easily break down and especially if your air conditioner has been running straight for five years without replacement. You need to replace them or risk having your air conditioner breaking down on at the most inconvenient time. You should take a photo that clearly indicates the make and model so that when you go to the store, you get something similar or close by. The condenser fan is also something else that might need replacement and only do so if you have identified it as a problem as its quite costly.
You can also check that the filters are clean. Cleaning the filters will get rid of dirt and other stuff that has accumulated on it. You can easily detach the filter from your air conditioner and clean it. Its best to always use clean water and a soft cloth. If you feel the dirt stuck is too thick to work on, you should soak it in order to make it loosen up. Make sure its dry before reattaching it to your air conditioner.
The condenser coils must be cleaned and cleared of all the grime that has accumulated. If its not cleaned, it makes it very easy for the compressor to break down due to overheating. Cleaning the coils is easy enough and you can get a special cleaning agent that you spray on then wipe out the dirt.
As a note, before you begin any repair work on your air conditioner, it goes without saying that the power must be turned off. You have to make sure you have unplugged from the power socket in order to avoid any accidents while working.