Car stopped running checked no injector pulse no spark, the mil lamp not on when key is on, found ground wire off and reconnected it but no start still

Bad ECM, crank position sensor, ignition module. Start there. Make sure timing belt or chain is good.

Check battery, ensure proper charge.

Test all under hood and under dash fuses with a test light or multi-meter. If the problem persists, focus on the Camshaft Position Sensor and the Crankshaft Position Sensor--Altimas are notorious for these items failing.