My early 2013 Macbook Pro Retina 15 started to freeze up a few days ago, the only way to get it (sort of) working is through holding the power button down and reboot. After a few days of investigation, I found out that if I have the Thunderbolt to Ethernet dongle plugged into the computer (even if there's no ethernet cable connected!), it will boot up and function perfectly normally.
I've tried to reset SMC and PRAM, as well as plugging in a MiniDP -> DP adapter, and a USB3.0 Ethernet adapter into my computer and booting up. None of them worked so far.
I've also reinstalled the system (tried Sierra, Mountain Lion, and El Capitan), made no difference.
Can someone please tell me what to do next? I'm a bit desperate. Thank you so much!

My early 2013 Macbook Pro Retina 15" started to freeze a few days ago. The only way to get it (sort of) working was by holding the power button down and forcing a reboot.

After a few days of investigation, I found that if I have the Thunderbolt to Ethernet dongle plugged into the computer (even if there's no ethernet cable connected!), it will boot up and function perfectly normally.

I've tried to reset both the SMC and NVRAM, as well as plugging in a MiniDP -> DP adapter, and a USB3.0 Ethernet adapter into my computer and booting up. None of these steps have worked.

I've also reinstalled the system (trying Sierra, Mountain Lion, and El Capitan) and none of these resolved the problem.

Can someone please tell me what to do next? I'm a bit desperate. Thank you so much!