I easily started up my John Deere 990 tractor and drove across a field. I killed the engine as I worked to place a chain around a fallen tree. Then when I got back onto the tractor it would not start. After towing it back to the barn I visually checked the different safety switches for foreign objects. The seat switch sometimes falls out of position but it was ok. I purchased a new battery with the same specs, 840 CCA, 1010 CA. I cleaned the cables and the opposite end of the ground wire to the frame. When I try to start I hear the fuel pump and solenoid but the engine barely moves at all, maybe one cylinder at a time. So I purchased a new starter, no difference. I have tried jump starting from the battery directly to the starter. I have tried with the solenoid wires to the tractor connected and not connected using a jumper wire from the solenoid to the starter (still worried about safety switches). Someone asked me to check the actual voltage readings...with the brand new battery installed in the tractor it is 12.6 and drops to 4.3 when starting, indicating a bad cable. But when I disconnect the new battery and try jump starting from my truck to the starter the battery is 14.3 and drops to 10.0 which should be more than enough. Truck amps are the same as the tractor. Soooo, now I am wondering if it is an electrical problem at all and out of ideas. The engine does turn a bit on each attempt and not seized up. What do I check next? We have made so many attempts...could the cylinders be locked with fuel? Even though the amps are good it seems like there isnt enough power to turn it over. I have looked at lots of other threads but nothing takes me to the next step. Thank you for any ideas!!!!