Not certain, but you either have a short or a double switch.

Can you turn on the light from two different locations?

If you have a volt meter, check to see that only one leg or wire has voltage, if you are reading voltage on the ground then you definitely have a short.

See Solar's first diagram.
More than likely, you have the hot wire and the neutral wire running directly from the panel to the light. 
Or, in other words, the hot is probably not running to the switch but to the light.
Cheap little volt sensor will tell you which wire is hot.
Then, hook it up appropriately.

And, let us know what happened.

First, get your wife's rubber dish washing gloves, and don't use a metal ladder, please.
120 volts won't necessarily kill you, but it will give you one Hell of a rush.
I love it myself....

Edit: I just reread what you wrote.
Quote:

On your meter, if the wires are removable, plug them into Red + Hot, to the hole that says volts probably 600 volts + and may have a triangle with a lightning bolt in it.
The Black is a Ground wire, and it will say Com. or Common and have a black, or possibly green hole to plug into on the meter, plug it in that hole, do not plug it in the hole that has only a number with an A mil/A behind it, that is for amperage.

Check the wires at your light first, turn the volt meter to AC setting. The red wire on the meter always goes to the hot wire, which is usually black, unless someone made a mistake, which may have happened in this case.

I think you said you had three wires, black, white, green, the green and white share a common connection, so both are considered ground if you look in the breaker box.
The Green/ground wire goes outside to the Earth, the white connects to the breaker box, which is connected to the ground wire.
So as you can see, only the black should have power.

Check for power, connect red+ to black wire, the black wire on your meter, I assume is black, connect it to the white house wire, it should read between 112 and 121 volts AC.
If not, turn light switch on, if you now get a reading, then there is nothing wrong.

Now if that is a failure, take the leads on your meter and check for voltage across the green and white, you should

not

get any reading whatsoever, if you do, stop and call an electrician, he will have the tools to find the short.

If none of the above applies, next go to the switch and remove the cover, use the leads like I described above, red to black etc, then trip the switch and check again, if no power is available, at all, remove switch and check again, you may have a bad switch , but they usually never fail in the on position.

One question, did the old light work fine at the switch before?
Or did you never use it?
Moishe may have a good idea, in that the previous owners used the breaker to turn it off and on.


OK, I'll stop here, let us know the results of the above listed steps, if I wasn't clear enough, again, let me know, I've been doing wiring for nearly fifty years, so I tend to assume people know certain jargon.

Okay. I used the meter and hooked up the wires appropriately. it works like a charm. But when I push the wires into the box in the ceiling and fasten the fixture to the bracket and turn on the power I keep tripping the circuit. When I unfasten it and let it hang down it works fine.

Well, what was the outcome?