I'm having the same problem. My saw is a contractor style with a start capacitor and a run capacitor. But both of the capacitors test to their rated capacitance.
The motor runs fine when it's not attached to the blade pulley and belt. But when the belt is attached, it can't turn the blade.
The blade and belt run free and easy when I turn them by hand.
The saw is clean with no obstructions.
The motor saw had been running fine. I made a couple of cuts one day, and turned the saw off to get the next piece ready. I made no changes to the saw, but when I turned it back on...nothing but the hummm and the click.
Any ideas?