I got my hands on the above grinder.

Atm, it doesn't work. I have checked the brushes and both seem to have loads of meet left.

How can i test what is wrong with it?

I suspect it is the switch. can i test this somehow before i go spending money for parts?

worth taking apart and checking connections. Basically go around checking continuity with you ohm-meter.

I had a Bosch one that has some solder joints that when they get really hot go open circuit. Not sure whether it is a design feature or not. It is now my "spare", got a new Makita one that is just awesome (if you get money/vouchers for Christmas).

If you take it apart you can bypass switch, be careful, and then you will know if it is the switch or not.

Usually a break in the cable, Couple of grinders i've had have outlived their cables...