Hello! It sounds like you have two FM2+ motherboards that are experiencing different issues. For the motherboard with the faulty RAM slot, it may be possible to repair or replace the slot, but it would depend on the specific damage and whether replacement parts are available.
As for the motherboard that's not booting properly despite the fans spinning, it could be a more complex issue related to power delivery or other components. In this case, a technician would need to diagnose the problem to determine the exact cause.
In terms of cost, it is difficult to provide an estimate without knowing the exact issues and the cost of replacement parts. Repair costs can vary depending on the complexity of the problem and the rates of the repair shop. It's recommended to contact local computer repair shops or technicians to get quotes for repairing your FM2+ motherboards. It's also worth considering the age and value of the motherboards before deciding to repair them.