Cooling fan not running
Could be lots of things I can think of:
Cooling fan motor dead (check with voltmeter to see if it gets 12V)
Thermostat stuck open and the engine never gets hot enough
Temperature sensor not working correctly
Short, bad or corroded connection
Shouldn’t be that hard for a mechanic to figure it out quickly.
Does it run when you turn the A/C on? Is the car overheating?
You should fix that