1995 Nissan Altima Car won't start

Have a 95 Nissan Altima that has run fine. It started this morning and upon shifting into reverse, it died. It now won't start, although it really tries and ALMOST gets there. I've checked/cleaned the distributer cap and all plugs and wires. It WAS low on oil, if that signifies anything although I've since filled it and problems are persisting. There is no engine knock when trying to start nor was there when driving recently. Battery is good (checked with lights, wipers, blower, etc) oil, ck engine, battery, and brake lights come on after it doesn't start. Any suggestion is greatly appreciated!