System will not sync

This xbox will not sync a controller. When you press the sync button it will not blink or sync. I have plugged the controller in to try to sync that way. But once unplugged its not synced. I have tried replacing the sync button assembly, the front power panel, and the side wifi panel. It still won't work. The sync button is functional you can press it and power button to boot the xbox into troubleshoot mode.