on old bikes, it's very common for the thermoswitch to fail, so the fan won't come on. replace switch, but first test fan and wiring by touching the wire on switch to ground. if key is on, fan should spin. also, inspect fan fuse, and be sure cooling system is full.
I'd suggest you physically check that the fan blade is not jammed e.g. by grass or a stone, and then check the fuse is intact. After that, you could check that you have 12V at the female spade connector on the thermoswitch (to ground) with ignition on; if not, there may be a broken wire or the fan connector block may be disconnected. You can connect a jumper wire to the female spade, to the chassis, that bypasses the thermoswitch and will make the fan run.
