@Kronos
Mob.1 mode never appears I have followed all the steps but I just can't do it

I tried instead done in this way and it is perfect the resolution is has 1920x1080p

in monitor I replace LCD Monitor and choose:
samsung syncmaster 20GLsi 1920x1080
then I choose:
1920p 50hz 56.25khz

I save
then I go to screen
I choose:
1920x1080

and it's perfect
everything works perfectly the monitor automatically configures the coordinates of the resolution.

I save
but on reboot everything is as before
it's as if he hasn't memorized anything.

if you need I can make a video to explain myself better
thanks again for any help i really appreciate it.

I did not think I would encounter problems with the resolution of the monitor