The most common reason for seeing this is the date and time not being current. Sometimes, when installing new hardware, the phone can revert back to factory settings. If you see searching in the top left corner, check your date and time to ensure that it is current. If it is not, change it and that should solve the problem!
If you continue to experience problems or your date and time are still current, open up the device again and re-connect the service antenna. If it is not properly secured or snapped down all the way, that is absolutely the reason the device is still "searching," and hasn't connected with your service provider. If you still experience issues, please feel free to reach out to our support team so they can better assist you.