'92 BMW 318 doesn't start

check the earth wire, sometimes they are lose enough to be problematic. Although if turning over and not firing up, does sound like immobiliser issue. Are you using the master key? although I'm not sure about 1994, should deativate once unlocked with key, unless after market alarm set up

It could be the key if the vehicle has EWS3, try your spare key.If the battery is full and you torn the key.do you get power on the thin wire to the starter?

battery is dead charge up battery.

battery is new i just hear one click from the starter area light radio horn windows all work ?

there may be a damaged wire coming from the receiver ring which sits round your ignition lock, this "reads" your key and allows the starter to turn your engine over so if there is an intermittant fault here that could cause your non-starting.

check the battery lead are tight, and clean for dirt. check the lead from the battery to the starter motor, if that ok. it could be the starter need replacing.

It is possible that you have the two small wires reversed or one is touching battery lead connection.

Clean the electrical contact points by the starter and chassey ground... remove and wire brush, then spray with WD-40, and replace.

More info needed. Is this a stick or automatic transmission? Check to see if you get power at the starter "trigger" wire (small wire on the front of the starter) If you don't, you might have a bad neutral safety switch (automatic) or a bad clutch safety switch (manual trans). You could also have a bad starter relay (under dash, left of steering column)
Charlie

Need more info....Does the engine turn over? Or do you get absolutely no response? Did the car operate correctly and then all of a sudden not work? Or was the starting problem getting worse and worse? If you get no response, I would 'hot wire' the starter to make sure it works. Run a positive and negative wire directly from the battery to the starter. If it turns over, you got a wiring problem, either the starter wires or the battery connections. If the starter turns over and it won't start - you have to find out if it is a fuel problem or an electrical problem. You can get a tester from any auto parts store to check if the spark plugs are firing. Just a couple of bucks. If there is no spark, you got an electrical problem. If the plugs are firing, you have a fuel problem. Disconnect the fuel line right after the fuel regulator. Turn the car over to see if fuel is coming out. BE CAREFUL. Let it squirt into some kind of container - don't let it shoot all over the place. If you aren't getting fuel, you may need a fuel pump. If you are getting fuel - do a compression test. You can get a compression tester pretty cheap, or some places will loan or rent you one. It doesn't really matter too much what the readings are - but they should all be about the same. If one cylinder is lower than the others, you may have have a cracked head, broken valve - you won't know until you get the head off. Even if the pressures are the same - if this problem was creeping up on you, in other words it got harder and harder to start - it could be worn out rings. How many miles on the car? I could be rings if you have very high mileage on it - like 150000 miles.