Old House, Wiring Problems in kitchen... HELP!?

That's a tough one... Here is my best guess:

The fixture was originally installed with a light/fan with a pull switch - not a wall switch. So you have one set going in from the breaker. Not being the last receptacle, there is another line going to the next outlet. Now the easy way to put in a wall switch is to run one wire to the switch on the wall, meaning the black carries the load to the switch and the white brings it back. So in effect you have a mess and can't just combine the whites and blacks without tripping the circuit breaker.

The easiest way to verify if this is the case is to uncrew the switch and see it there is a black wire and white wire attached to it instead of 2 black. If so, then you need a tester to find out which set is coming from the box. Then test the other two wires to see which one goes to the switch.

Good luck.

To answer part of your question, The switch uses 1 black wire & 1 white wire. If you connect all blacks & all whites togeather then you are shorting out the circuit thru the black to white wire thru the switch since the black is hot and the white would be neutral except the switch uses the white wire to power the light.

You should have a black wire coming in (From panel), Conected to black going to switch, White coming off other side of switch ( White wire Should be marked with black electric tape) Going back to light & connected to black wire on light.(also marked with Black electric tape.) White wire from light goes to white wire going back to electric panel.

As far as the extra black & white wire, You could check for an outlet or light that is not working unless someone burried the other end of that line behind a wall.

Was the fan on a 2-way switch? A 2-way switch is when you can use two switches to control the fixture. If that is the case, get a voltage tester, and (with all of the wires disconnected) find out what wires are hot, and when. Put labels on each wire and take notes. You should have a wire that is a "common" meaning it can be either hot or neutral depending on the position of the switches.

This sounds normal. One pair will be supply (hot), one pair will be continuation to other circuits and one will be the switch. The switch white wire should have been taped to show black. I f you have an ohmmeter measure AC Volts fist (with the power on). The wire that shows voltage will be the supply. Mark it and turn the power off. Now measure another pair with the ohmmeter on "ohms". If it is the switch pair, it will show shorted (zero ohms) and infinity with the switch off. The other pair will be other circuits.

Now connect all the blacks together with a marret. It is a good idea to tape the marret. Take all the whites including the one to the light and except the one from the switch and bundle and wire those together. You are left with the black from the light and the white from the switch. Tape the white from the switch to identify it for the future. Now connect those two together. And it should work when you put the power back on.

Just a guess. One of those white wires is a switch leg. That is a hot wire from a switch. You are connecting it to the neutral wires, causing a short. How it was wired before would be the clue.