I pulled the engine computer and put it in a bmw im trying to get running,when i put it back in my running bmw now it wont start

Hello, too hard to know what's going on. But a terrible terrible terrible idea regardless. Why would you do this? How do you even know that it's possible to do what you're doing successfully? You haven't proven anything, engine processors must be programmed upon installing in vehicles. If you don't have the proper equipment you're only causing more problems. You can actually cause a power surge that damages components. You can have a wiring problem. You can have blown fuses. I am sorry to say that it does not appear that you are properly equipped to do what you were doing to this vehicle. Seek professional guidance near you. There is absolutely nothing I can do to suggest anything else that will help. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops