Ok, power to the switch and no trigger switch.

See the largish brush covers on the sides (#9)?
Unscrew them one at a time and inspect the brush (don't rotate them 180 when you put them back, they are set to only work one way).
With the brush out, a blast of compressed air is nice to clear out and built up dust.

You might also want to work the speed dial back/forth a bit to clear it up.