Engine Mechanical problem
1994 BMW 525 6 cyl Two Wheel Drive Manual 199000 miles
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The car had been driving perfectly, and then today i parked it and went to work. came back out and tried to start it but it would not turn over. there were no signs of anything going wrong. the battery works fine. what could break so quickly that would stop the car from starting?

With the information provided(Thank you for trusting us to help you) there are too many things it could be to list here in any type of order, so lets start with what has been done, and I assume you have not done anything yet other than an attempt to start the car and a visual inspection. Three things are necessary in order for internal combustion gasoline fueled engines to run, fuel, spark and compression. I will eliminate compression because we know the car did run, that leaves fuel and spark which in this case go together. So here goes with a silly question, is there fuel in the tank? Next item to consider, is the fuel pump working and is there sufficient fuel pressure? If there is spark, then a bit of aerosol parts cleaner sprayed into the intake should make the car start if only temporarily. If this proves true then fuel is the only missing component, and we are closer to getting you back on the road. If not then there will be a need to go further and I request you send me a private message to coordinate this repair as I find having to type back and forth too slow and awkward.

it wont let me make a private message post until i have made 10 posts myself. but i did try the parts spray, and the car started for a few seconds. what now?

This seems like a fuel pump issue. Check the fuses and look at the legend inside fuse box cover to get the right one and check it's integrity. Replacement of the pump and filter might be required, they are next to the fuel tank under the car, first check for power at the fuel pump. If no power then the fuel pump relay is next thing to inspect/replace, it is in the E box under the hood to the rear of the shock tower. There are four Phillips screws holding the cover on. The two square plastic relays in the center of the box, about 1" by 1" are the main and fuel pump relays, it will be either orange or green, the white one is the main relay. Remove it and tap it on something several times and try it again. Let me know how this works out, I will be standing by.