Welcome to JustAnswer, my name is XXXXX XXXXX I'm here to help get your problem resolved. Please feel free to ask follow up questions, it is part of the process, thanks.
They are probably right. Your computer may have been corrupted when the battery was swapped. You will need to get it to the dealer for a diagnnostic which will be about $100 and the probably another $100 if it just needs the flash though it may be less.