Are you saying that you replaced the light switch. Flipped the breaker back on, the lights worked and now at some point they stopped working?
If the lights didn't work after replacing the switch, make sure the breaker is actually flipped on all the way. Flip it off then back on and make sure it's all the way. When I was working electrical, we got a call one time similar to this. Turns out a lady flipped the breaker, but it wasn't all the way on.
