'94 MGM Engine

OK my engine died so I bought a used engine, 80K, and put it in. The problem is I drowe it for 2 days, and it just stalled on me in the middle of the street. I can not start the car now. When it just died I was able to start it, but it would stall immediately. Do you guys think it might be a bad oil pump or something, and how to check it out, or did they just sell me a bad engine???
P.S. My check oil light came on before it died.
Any suggestions would be appreciated, spent a lot of money on it...
Thank you.