Chosen Solution
The USB input and HDMI input are not working, is there any way to fix it?
Best case: Your I/O board cable is not seated right or has been damaged. MacBook Pro 15" Retina Display Mid 2012 I/O Board Cable Replacement Otherwise, it’s likely a bad I/O board itself. MacBook Pro 15" Retina Display Mid 2012 I/O Board Replacement
