[Rich Biebel]

I’ve never seen a belt break on a 5500 diesel.
If it has no output it will shut right down.
Put a voltmeter on the machines AC output wires as close to the machine as you can get. Terminal strip at rear left upper corner under cover is AC output.
If it starts even momentarily you should see AC output.
If no output the brushes are the first thing to check next.

Top cover off allows you to see the belt. It’s at the back of the machine, look straight down.

Brushes are the same ones used on gas machines. They wear or fail regularly. If they did fail you will need to sand the rotors slip rings for sure. A piece of sand paper taped to a wooden stick works well. I use paint stirs and cut strips to fit.
If brushes are ok it gets more complicated.