Anyone familiar with tetra pond pond pump troubleshooting?

I have a Tetra pond 2500 pump( above ground and a submersible part) it was running fine all spring and summer until today, it acts as if there is no power going to it, although there are no GFIs tripped and there is power at the outlet. Is there a sensor or somthing that would cause this? Or possibly a way to reset the pump? Thanks in advance for any suggestions.