I am connecting a new Hampton Bay ceiling fan to a 3-way electrical circuit (2 black and 2 white service leads to the fan). Instructions say to connect both the blue and black leads from the fan to the black power source. Since I have two black power leads, I tried putting the blue on one and the black on the other; no luck. If the two black power leads touch each other, the breaker blows. What am I missing? Thanks. Lou

By" 3-way electrical circuit", I assume that you already have a pair of 3-way switches installed.

By "2 black and 2 white service leads" I assume that you have two 2-wire cables coming into the ceiling box, each with a black and white wire.
One of those cables will be the power coming to the box. The other will be the switch loop. The switch loop takes the power to the switch and brings it back if the switch is on.

If that is correct, the black of the power cable should be connected to the white of the switch loop.

If these wires have been disconnected you must determine which is the power cable and which is the switch loop and reconnect.

If you want both the fan and the light to be controlled by the switch, connect the black and the blue wires from the fan/light to the black of the switch loop (this is not advised).

If you want only the light to be controlled by the switch (this is the usual) connect the blue from the fan to the black of the switch loop. Connect the black from the fan to the black of the power cable. That's the one you already have the white of the switch loop connected to. The fan will be controlled by the pull chain and the light will be controlled by the switch.

What was there before the fan and how was it connected?

Ceiling Fan Wiring - Ceiling Fans N More