Time to call in an electrician. Sounds like there is some ground fault somewhere. You are not going to be able to fix that yourself.
@Keepit, there are ways to run power thru the switch box, and run a separate feeder to the light fixture with a 2 wire cable. I've seen black tape on a white wire in those cases, to denote that both wires can be "hot", depending on how it is wired. In fact, I think most electrical codes require a white wire that is used for "power" to be labelled with black tape. It is not a common way to do it however, usually an afterthought or modification to existing wiring. Proper modern wiring would not be done that way any longer.
@Keepit, there are ways to run power thru the switch box, and run a separate feeder to the light fixture with a 2 wire cable. I've seen black tape on a white wire in those cases, to denote that both wires can be "hot", depending on how it is wired. In fact, I think most electrical codes require a white wire that is used for "power" to be labelled with black tape. It is not a common way to do it however, usually an afterthought or modification to existing wiring. Proper modern wiring would not be done that way any longer.