1995 Mercury Mystique Engine fan not working

Engine Cooling problem
1995 Mercury Mystique Automatic

My car is overheating and the engine fan is not working. After the thermostat was replaced the fan started working. However, a few months later, the fan stopped working and the car started overheating again. The thermostat had been replaced a year prior. Could there be something causing the thermostat to stop working? Also is this the reason the engine fan is not working or could something else cause the fna stop working?