No power to light switch
How many wires are in the box? If you only have two (1 white/1black) you have what is known as a switch leg.
Do you have a ground wire in the cable that is terminated under a screw at the back of the box.
If so, you can check for voltage incoming by measuring from the box to the white wire. Then, if you operate the switch to the ON position the voltage should leave on the black wire.
This is assuming that the wiring was done according to convention.
Photos are the best way of explaining a problem, if you are unfamiliar with electrical terms.