Could be multiple issues.
Thermal sensor could be fried.
Pump could be out
Heater core could be toast, but that is most likely tied ot the thermal sensor.
What about a faulty power connector? Or, did you yank and put a meter on the fuse? I had a fuse blow one time and it didn't appear blown, which really annoyed the crap out of me. If I had metererd it out, I would have still been angry because I had no spares, but at least I would have known my problem.
Is this unit squirting anything out? Noise when you hit the switch(pump engaging)? Been a while since I used mine, so any dummy lights coming on? Can you meter out if it's drawing voltage?
The other sounds like the nozzle is clocked and the tube that runs through the heater core has rusted or corroded. It sounds like everything else is fine if fog is coming out of the machine.
Time to do a franken-fogger? I'm guessing based on age, these are out of warranty. Bad idea.
Let's wait for others to chip in. I'm just a sound guy. What do I know about lights and foggers...
I get the feeling you could do the repair with the right parts if you knew where to begin.