Alright, I've been fighting this battle for almost a week now. My 2004 duramax won't start, it won't crank over, I have no glow plug light and no check engine, I have power in the cab, all my lights on the dash light up and my gauges read, I also have headlights, the only indicators on the dash that come on are the battery light and the security light. This all started last Friday when my alternator went out on me. I bought one after work that same day and swapped them that night, I started my truck to see if it would charge but I still had the same no charge issue, so the next morning I took the new and old alternator and went to the local parts store and had them tested, the new one was good, so I go Hoke and put it back in and I go to start my truck and I've got nothing, won't crank no gp light and no CE light. I've checked fuses I've checked power at them, I had a scanner hooked up and was given a p1621 error code saying the long term memory module needed to be reprogrammed. So I pulled the ecm to have it tested and was told that it tested good on the bench, I'm at a loss of words right now, I have no idea what it could possibly be, I'm very disappointed with this truck so far. If anyone has any sense of direction please I'm all ears.