car shuts off when put into drive on 2000 Pontiac Grand Prix GTP

My son was driving his car and it shut off. He can start it but once he puts it into drive it shuts off. He had it towed and a mechanic told him he needs a new engine. Does this seem right? Please help!! THanks. I know nothing about cars. I told him he should get a second opinion before he decides what to do.

Asked by for the 2000 Pontiac Grand Prix GTP
Sounds like a security problem to me. Try another Key