There are 4 main types of electrical problem with a Power tool, Cable, Motor, Switch or Speed control.

The cable and switch can be easily checked out with a meter, as can the motor.

If all of these seem OK, then the speed control PCB may have failed. When the board fails, the drill just does not work at all.

Before replacing the board, it is worth blowing some compressed air through the speed Knob, as these can get full of dust and that will stop the saw working.