My ceiling fan stopped working.n I replaced nthe fan and still not working. I think that it is in the light switch. The old switch has a black and white wire on different sides of switch.. The new switch the wires go on the same side. Which wire goes where

Is it just a basic on off switch?

Sounds like you have a switch loop from the ceiling box. If so, the white wire should be taped black. Check to see if you are getting power to the switch and then through the switch. If power at the switch and not through, take the new switch and connect the black to one terminal and white to another. Doesn't make any difference on a single pole switch. If everything works, put black tape on the white tape or use a black magic marker to make the white black. That way the next person will know that the white is hot.