starter problems

[JackFish]

She fired up as per usual today, with the normal coaxing due to the cold, but...vroom, vroom and died, and then refuses to turn over. The relay clicks quite healthily and was new last summer. I check the battery, have a booster box that does 2, 10 and 55amp boost. battery looks good and the boost setting just gets a click.
I then took the positive cable from the booster and touched it to the cable going from the relay to the starter, nothing. It's also a new cable.
So is my starter dead, and why would it die so suddenly?

 

[addo]

Did it actually start and run? Maybe the pinion gear is jammed? Other than that, broken brushes, poor undercutting, internal severance. Remove the starter and "floor test" it.

 

[JackFish]

Yeah, it actually fired up an ran for bit, but as it's cold sometimes it takes two or three times to get going, so that was normal. Haven't got the choke high-speed cam set quite right yet.
Jammed pinion gear? OK, how to check and fix? It's possible.
I was able to grab the power steering pulley and belt and rotate the engine a bit to check for internal seizing and eliminate that.
So to floor test, I have a good battery and use jumper cables to connect to the tab (+) on the starter and somewhere on the frame (-)? What should I expect from a good starter? Violent jumping about as it cranks?

 

[addo]

OK, if you can turn the motor by hand, the starter pinion isn't wedged against the flywheel.

To test the starter off the car with jumpers, I clamp the ground cable to a bolt ear and the battery, the positive to the battery, put my boot on the starter and touch the jumper red to the threaded post. The pinion gear should lunge forward and start spinning immediately. If it doesn't, there's a problem.

If it turns slowly, then there may be damaged windings or internal conductivity problems. That cold must make operations like this, less fun (specially when you skin a knuckle)! Nearly 38°C here today.

 

[XFlow_Fairlane]

what he said. it might also be possible that you have a poor ground somewhere in the starting circuit.