No Electrical Power

I have a 1994 XJ Sport, 2WD, and every so often, when the car is off, all electrical power will stop. Lights won't work (interior or exterior), buzzer doesn't sound when the door is open, and, well, it won't start, either. Occasionally I can get the electric to come back on by fiddling with a few things. I recall once when I moved the shifter (it's an automatic, and when it does this, it will move freely without the brake applied), everything came back. I've replaced the battery and terminals, and now I'm not sure where to go. I'm a college student without a job (and thus cannot afford to take it to a shop), and even though it's on loan to my parents (they don't have a car), they can't afford to take it anywhere, either. But I've done quite a few repairs on this car, and I've got time to work on it. Does anyone have any idea where I should start looking for a problem?

Any help would be appreciated!

when you lose power does your clock read 12:00 when it comes back on?

On my radio? Yes, it does reset.

you have a bad connection somewhere or your vehicle is possessed

Is there an easy way of going about finding this?

It's difficult to troubleshoot, as it only happens every once in awhile. But when it does, I'm stranded until it decides that it wants to work.

Ok, well start at the battery, make sure the clamps are tight on the posts. then follow the ground cables, make sure the conections to the body/frame/engine are secure. then follow the positive, make sure the connections to the alternator and the power distribution center (box with the big fuses under the hood near the battery). then go through the pdc and check the fuses in there. take a look at that stuff, see wht you find.

if you are lucky it will be a loose connection somewhere, you'll have to hunt it down. If you are unlucky it will be a relay or a short somewhere, if that the case, well, start looking at connections.