I'd say either your power wire to your fan has an open break in the circuit, loose wire, connector came apart, blown fuse or whatever. Or the thermal switch that turns the fan on and off has failed. The thermal switch operates by completing a circuit [closing] when reaching a certain temp-180,190.195 ... then turns off [opens] when the temp at the sender goes below a certain temp. Some are in the radiator fins, some in the water jacket. Usually the power goes to the fan and then grounds through the switch to complete the circuit. If yours has one wire going from the fan to the sender at the water cross-over, you can disconnect the wire at the sender and connect it to ground and your fan should fire up. If your circuit has the power going to the switch and the on to the fan you can disconnect the two wires from the switch and connect the two ends to get power directly to the fan. Or maybe the fan itself has given up the ghost.

Always a good Idea to have a toggle switch someplace to turn the fan.fans on manually, just in case the thermal switch goes kaput.
When I bought my car the fans came on when the ignition switch was on. Didn't like that so I put a switch in the water cross-over. While driving up Vancouver Island one day the car over heated, I pulled over and the fans were not working. the thermal switch failed. I did not have a toggle switch at that time and had to scrounge a piece of wire from a passing motorist to by-pass the thermal switch and get the fans to operate.