Diesel Bombers - Engine Hard To Crank Over

I have a 1999 7.3 diesel. I removed the injectors to replace the o-rings. I cranked over the engine to clear out the cylinders and i also took an air hose and blew out the cylinders just to make sure there was nothing in the cylinders. I reistalled the injectors and put everything back on. Went to start the truck and it would hardly turn over like something was blocking it and then it would sound like the batteries were dead. I hooked up jumper cables to see if that would help but still the same thing. i was told to take out the glow plugs and crank the engine over to see if any fluid came out .I did that and nothing came out i reinstalled the glow plus and tried to crank the engine over but still cranks like something is blocking it. can it be the starter just being weak to cause it from not turning over normal or I'm I just missing doing something. I have been working on this for three days and need help badly.