Bathroom exhaust fan wiring ?

Hi I am replacing an exhaust fan in my bathroom. Foolishly I did not take note of how the wiring was set up prior to removing the old fan. The old fan had 2 sets of wires attached to it so now I have 2 black wires coming into the housing and 2 white and 2 copper. as well as the black and white from the fan. I put all the blacks together and whites and the fan runs with the switch off and the bathroom light works properly. If I turn on the switch the circut blows. I tried black and white from the opposite wires and the circut blew as soon as I tried to switch it on at the fuse box. So now I dont know what to try. Any advice ? nthx