BMW Repair: BMW318I 1992 MODEL, window switches, sandpaper

Question
my power windows are not working,fuse is ok, the circuit breaker is on, power to the circuit comes up and cuts off on its own with the greater time without power.is there any relay liked to the power? what could be the problem.

Answer
the window switches on the late 80's/early 90's BMW's were prone to failures.  They can be expensive to replace.

If you pull the switches, they can be carefully taken apart from the back, and the connection points cleaned with ~500grit wet/dry sandpaper, then reassembled and reinstalled.

See if you have power at the switch.  if so, you may want to try to clean one of the switches, then either clean the remainder or buy new.