Complete power loss w/key turn
 

My daughter drives a 94 Century (120+ K) and it was running great, no issues to speak of. Thursday morning she was advised that her brake lights were stuck on when the car was parked in school lot. Drained the battery. Battery was very old so she got a new one proper size installed; car started up and drove fine. Later that evening it started up and drove no issues.
Next morning; NOTHING; No Start. I checked and when door is opened interior lights come on, insert key and door chime rings. Turn key and there is nothing at all, a total loss of power, lights go out, door stops chiming but nothing. Starter never engages, no noise, no attempts of the engine to turn, remove key and lights return and door chimes!
PLEASE HELP!

Two things come to mind, the first is , does the vehicle have an anti-theft system in it?
Second a thorough check of the battery cables and connections would be a good place to start. By check I mean remove the cables and check underneath for corrosion. GM cars were good for corrosion under the positive cable at the battery.
If none of these help let us know and maybe we can come up with additional checks for you to do.

We've only had the car since last Oct/Nov and I don't drive it so I asked my daughter. She said that it does not, there is no indicator light on the dash anywhere and I don't remember reading anything at all about it in the manual (read thru manual night it was bought). So I don't think it does have any Anti-Theft system installed (factory or after-market). I'll check connections but since it does have power to interior lights and door buzzer then as soon as the key is turned (not to start position but only to accessory position) all power is lost, it leads me to believe that it is a switch of some sort that is shorted out.

OK ,now we're getting a little more info. The ignition switch is located under the dash and attached to the steering column. It does sound like the switch loses contact in certain positions and when that happens the only thing to do is to replace it. Depending on how determined you are will decide if you replace it or have someone else replace it. The switch itself is activated by a long rod from up in the column where you turn the key.

Just last year I replace the ignition switch on a 92 Taurus which was real easy to do. If memory serves me right the GM switch is a bit more complicated at least was in the late 70's. With the Ford it was a matter of disconnect battery, turn ignition part way, insert small punch and pull. The whole switch just came out and the new one slid right in.
Please tell me that it is something very similar to that with GM's!

If you were going to change the ignition key tumbler, it would be similar, however , you are considering changing the ignition switch assy and they are two different animals.
Believe it or not the ign switch is in the same place on both vehicles, UNDER THE DASH ATTACHED TO THE STEERING COLUMN. I know you didn't want to hear this so , just try reading it without moving your lips and you probably won't hear it.
Sometimes what I suggest is that you go to your local auto parts store and ask to see what the switch looks like. Then you can decide if you care to do it yourself. Its not a difficult job if you can bend like a pretzel and feel no pain. Other than that it's a piece of cake.