Does the problem appear to be with the motor itself, or is just the computer display acting up? Do you keep the treadmill in a relatively cold place in your house?
I keep my treadmill (same exact model - Pro-Form 750CS) in an unfinished basement, and when it gets too cold down there, the unit won't start...has nothing to do with the motor, just the computer that controls the motor acting up.
If I set up a space heater to warm up the computer console (note again: the computer console, not the motor), the unit operates properly.
I know it sounds stupid, but it took me three years of fighting with the machine until I figured this out and it works 100% of the time.
Hope this helps.
Alex, February 2007