Old, all metal belt sanders are still great tools. To fix this, you're going to have to disassemble this tool. Here's what I think: Pull the brushes and look at them. They should be shiny and slightly curved on the ends that contact the armature (actually the commutator). If one or both are powdery and the brush spring is blue and has lost its springiness, the armature or field coils or both are no good. However, if the brushes look good, pull the armature out and use some fine sandpaper on the commutator - the copper bars on the brush end of the armature. Clean 'em up! Then make sure the brushes can freely slide in their holders all the way down. Next check bearings or bushings are free. WD-40 is the pixie dust of choice. If all is O.K. and there are 2 wires coming down from the field coils to the brush holders and they are O.K., put it back together. It should work! I've been in the power tool repair business for 49 years. I have an old Stanley belt sander that I still love.