Trust me - you need that motor that BobBecky posted. I have the same amazon link in my account still.
Mine did the EXACT same thing last summer. I even started with twist ties because holding the wires seemed to help (for a couple minutes).
Install was 3 minutes - works like a charm. You have a 50/50 chance of putting the 2 power wires on the connectors (They are not marked). The wrong way spins that fan backwards so make sure you know which way it is suppose to turn first.
Trust me on this one