1998 Audi A4 2.8 Quattro 5 Speed 139k miles. My son was shifting from 1st to 2nd when he said it sounded like the front end dropped out. All the dash lights came on and the vehicle shut off and will not restart. Had a mechanic look at it and he said it froze up, he couldn't get it to turn at all. Any ideas?
My son wants to replace it with a twin turbo engine. Is that even possible? I hear it would be mega expensive with potential big problems. Please help.

Thanks