Engine Mechanical problem
1993 Infiniti Q45 V8 All Wheel Drive Automatic 155000 miles

I have a 1993 Q45 and had just got done replacing my BCM because none of the windows or seats would work. got everything working and drove a 1/4 of a mile to gas station to fuel up but car started sputtering very bad but barely made it to the pump. i got gas and got ready to start it and it just made a click sound at the starter. I had just brought new battery earlier that day, so i know battery was good. i had to pull car back home and i took starter off and got it tested and it was good. My anti-theft alarm light is not coming on at all when i take key out of ignition now. I replaced all the anti-theft relays (3) and the anti-theft control module. Replaced the starter relay also. I tried to turn crankshaft pulley with a socket and it would only turn a 1/4 turn and stop. Clockwise and counterclockwise and stop.
Do u think my engine has locked up or could it be a starter kill on the anti-theft system that the book isn't telling me about. Could it be the timing chain broke or what. I do all my work myself and need an experts advice on this one. Don't want to start taking motor apart if I don't have to. Can u please give me some insight on this one because it's got me puzzled.

Thanks in advance for your expert opinion!!