I would really stick with an in-ground motor, above ground motors don't really need to be self priming since water wants to basically pour into the motor, even still if you get air trapped in the pump part by accident it can still take a while for it regain it's prime on it's own. You can typically make it start much faster by loosening the lid until water starts to squirt out and then re tighten the lid. I would just take your motor to a repair shop it could be a simple problem but could get worse if let go for too long. your contact switch could be rusty, the fan intake on the motor might be jammed with debris etc. Regardless if you do need a new pump&motor an in-ground motor should be used