Lights go on, but engine won't crank

We have a '89 Mazda 323, single overhead cam, 1.6 ltr engine, 4spd manual 2wd. The problem started with changing into second and third gears, the engine would bog down like it wasn't getting fuel, and then it would go on as normal. This lasted a couple of days and then it bogged down and died. The engine would then turn over but not catch. We replaced the fuel filter, checked the fuel pump. Then the car would not even turn over. The dashlights come on but the engine will not even turn over. We replaced the spark plugs, distributor cap, and rotor. Took out the starter and soloniod, alternator, and battery and had them checked at the parts store. All came out good. We are at a loss as to what it could be. After talking with people and looking at the site, I have four possibilities: catalytic converter, ignition starter switch, clutch switch, or the "brain box". Could it be one of these or something else? Thank you ahead for your time and efforts.