MBP Retina mid 2015 only works when connected to an external screen

Hello all,

I have MacBook Pro Retina from mid 2015 (16GB RAM, 500GB SSD, Sierra) that freezes if I use it without any external monitor connected. It logs in and freezes after few seconds. But if during these few seconds I connect an external monitor, then I can use both screens (and even in "extend" mode, so the MBP screen works on its own).

I've tried erasing my SSD and reinstall macOS, but the problem is still there. I'm actually configuring the MBP again connected to my TV via HDMI.

Any ideas what could it be?

Thanks!

Jose