I have Ubuntu mate (based on Ubuntu 14.04.2) on my Lenovo laptop. I also have an LG monitor connected to the VGA output. I am experiencing something weird with this set-up.
The problem is that when I turn on my laptop with the monitor connected, the screen freezes blank right before the login screen and it will remain that way until I disconnect the monitor (there fore I can't login). If I disconnect the monitor, the blank screen unfreezes, the login screen appears and I am able to login successfully. I can then re-connect my monitor, the OS recognizes it, and everything works perfectly from then on.
I have searched the web and found nothing similar. I haven't searched the docs because I don't have any idea of what docs to look. Anyway, I'm really lost here.
By the way, this set-up worked perfectly until two weeks ago, when I had (pure) Ubuntu 14.04 installed. It all started when I installed Mate.
Any help is appreciated. Thank you very much.