Late 2013 15" rMBP won't restart

[ip67]

Hello, I'm trying to figure out why my Late 2013 15" rMBP won't restart by itself in clamshell mode if I have my Dell P2715Q monitor plugged into it via DisplayPort. I have to open up the lid and force the computer off by holding down the power key on the keyboard, and then turn it on again. I'm also using an Apple brand Thunderbolt to gigabit ethernet adapter. The monitor does lose signal when I attempt to restart, but the computer just doesn't want to restart for some reason.

I'm using macOS Sierra 10.12.1

I can restart it fine if I'm using the computer by itself without an external screen attached.

Thank you for any help offered!

 

[jerryk]

My 2015 15" rMBP sometimes has issues. I find that it works best if the monitor is off until after I connect all the cables. And sometimes I have to open the lid, wait for the mac to discover the monitor, and then close the lid. I have not had to reboot to connect recently, but did more often with El Captain.