Cannot get ubuntu desktop

I am a newby with Raspi, i had installed Ubuntu mate on my raspi 3 , and it was working well, i was getting through SSH connection with Putty from my computer for terminal command.
Then i installed tightvnc server on raspi and RealVnc viewer on my computer.
trying to modify the boot file I think i did a misrake....
Tehn i lost my desktop Ubuntu and start have problem to connect with Putty.
I finally recover the connection but not the Ubuntu desktop, the only connection is through Putty (SSH) when it work or directly through the MDMI screen connected but just with the terminal.
The screen is only flashing and i have to do cntr-alt-F1

I think the issue started when i added these line in the xstart file

gnome-panel &
gnome-settings-daemon &
metacity &
nautilus &
gnome-terminal &

after it was asked (dont remember the website that proposed it!!) to install gnome
but doing so the raspi-config screen popup ahd warned about getting two desktop so I choosed the " lightmd GTK " (think this is write correctly) AND THEN START THE PROBLEM...

How could i solve these issues ??