m4800 k1100m external monitor hdmi/vga linux

Hi,

I'm having trouble connecting this laptop to an external monitor and achieving one extended monitor.
I often get black screen after at login or after login.
Tried with nvidia drivers (connected through hdmi) or without (connected through vga).
Sometimes it actually works, but most of the time I'm just fighting to login..

I'm using the latest Ubuntu distro.

Anyone has advice on how to get this to work properly?

Thanks,
Michael