|Do an open case visual inspection. of the fan is not turning, follow the wire and make sure it is plugged in. If it is plugged in and the wire looks good (no breaks, bare wires, or pinched between components) but does not work, replace the fan with a new one, they are really inexpensive.|
If a new fan does not work (uncommon but possible) then look in the fan's package to see if it comes with an adapter to power it directly off one of your power supply's plugs and use that. It will run at 100% and be noisier but it will work for all except the CPU fan.
If your GPU does not cool down significantly, you may need to either speed up it's fan (software) or try reseating it's heat sink with a clean application of thermal compound (not too much and on clean surfaces) and reassembling it.
You have to be a little bit crazy to keep you from going insane.