Probably because you either unplugged the camera module or you broke something. That's why people who don't have experience repairing cellphones shouldn't try to repair them themselves.
Now you have to find a repair shop that will repair a phone that you've already worked on (most won't, because they have to check everything to find out what else you may have broken). And the repair will be expensive, because it's going to take them a long time to check the entire phone out. (You don't save money replacing the screen yourself - you end up spending a lot more than if you had brought the phone to a repair shop to have the screen replaced.)