We have a 1993 190E that wont start. Quit while someone was driving it so we parked it until we could work on it, started it and it ran fine for 5 minutes and then quit. Hasn't started since. We have done the following:

Changed distributor cap
New rotor button
New coil
New crank sensor

The plugs are not getting any fire/spark, been told it could be the security system, and I have checked to see if it works (by rolling the window down, locking it with key, pulling plunger on inside and opening the door) and there was no alarm to go off. If it does or doesn't have a security system, what are some common problems? Thanks!