If that's the lathe I think it is it is about the same as the other metal mini lathes (variable speed DC motor mini lathes from Grizzly, HF, etc.).
Several things to check beginning with the switches and the connectors for the wiring to see if they are loose or corroded, maybe the motor brushes if you have significant time on it, and maybe the most likely being the speed control potentiometer if the others check out (which can cause erratic speed and operation of the motor).
Those little fuse holders can also cause trouble - simple as they are there is nothing the Chinese cannot make poorly.
If all those check out and obvious things like the electric line(s) are good and the wall outlet good then the problem may lie with your motor controller itself (that would be the circuit board). Several problems with those boards (if they are the same as the Grizzly, HF, etc. boards) are the MOSFETS and sometimes bad solder connections. There are other things that can cause the problem such as the rectifier circuit in them (which can be found with a simple multimeter to see if it is putting out AC or DC voltage) but not as common. They're pretty easy to fix if you can do simple electronic soldering to replace the defective parts.
If you trouble shoot inside the controller box with the cover off do yourself a favor and unplug it first then put it all the way back together before plugging it back in, even the DC side has over a hundred volts which can give a fairly stiff shock. It takes a little longer that way but is much safer.
