Im pretty new to this I will admit and I need some help, so I took my bf's 2000 ls to a shop where they installed a b20b , (just a replacement engine ) so when I went to turn on the car it appeared the battery was dead. After several charges, nothing. The lights worked, but the engine wouldnt turn. They decided to keep the car an extra day and said it might have to do with the alarm system. What? How can this have happened?

 

They may have forgot to connect one of the ground wires. That's the first thing I'd check anyways.