must be frustrating to have everyone telling you you wasted your time coming here. actually the advice everyone is giving you is correct. you do need to have it properly tested.
let me try to shed some light on the problem. the possible problems are limited, but the one step you took is actually is the most revealing to us. you turned the fan switch on. that basically rules out the thermostat because neither switch onboard the thermostat will turn on the indoor fan. a sudden problem with low voltage wire is not likely. that leaves the fan motor, the fan capacitor and the fan relay. any of these could be the problem.
there is one diy thing you could try. make sure the thermostat is in the 'off' position (if the compressor outside runs without the fan, compressor damage can occur). turn the fan switch on and listen for a hum at the motor location. feel the motor to see if it gets warm. heat can build up quickly when a motor stalls, then it will eventually open its circuit internally, a built-in protection device. when it cools, it resets and tries again. a defective capacitor will result in the same symptoms. if the motor hums and gets warm, turn the power off to the unit and replace the capacitor. (WARNING - IF YOU ARE NOT 100 % SURE THE POWER IS OFF TO THE AIR HANDLER, KILL THE POWER TO THE HOUSE. THERE IS DANGER OF ELECTRICAL SHOCK AND POSSIBLE DEATH. IT IS BEST TO VERIFY POWER WITH A METER.) it will be mounted on the housing. two wires connect to it. disconnect the wires and remove the capacitor and take it to a supply house to match it. it is a relatively inexpensive part and worth a shot. a significant percentage of times motors fail, this is the problem. sometimes it is related to maintenance issues, sometimes not. without training, parts swapping is all you can do. after changing the capacitor, if it still hums and gets warm, you will need a motor. if the motor is cold and does not hum, it may need to be replaced, but testing will need to be performed to determine the actual cause of failure. without a way to verify the motor, swapping the circuit board is not as cheap and not a good gamble.
if you are uneasy about any of these suggestions, just follow the concensus and call a service company. the repair may cost you anywhere between $150 to $450 dollars, depending upon the problem and the company. good luck.