I bought a new monitor and it is working fine,but every time I am at the grub screen the monitor tries to fine tune and adjusts itself,if I open the monitor after the grub screen nothing is adjusted and I see the display.I think I have to change the grub screen resolution.I found this : Step 1: find the preferred mode Reboot and press and hold shift to display your grub. Press C to enter console mode. Type vbeinfo this will display various stuff how grub recognises your display. At the bottom is "preferred mode" - in your case it should say 1200x800. Note down the value. Note: sometimes, some buggy video cards incorrectly give Grub the wrong preferred resolution - if the preferred mode is much higher than you were expecting, then select the nearest mode in the list displayed that you were expecting. Press ESC to return to grub and press Enter to boot. Step 2: Setting the resolution in grub Reach for your terminal and type sudo nano /etc/default/grub find the line #GRUB_GFXMODE=640x480 remove the # and change 640x480 for the preferred mode you wrote down. e.g. GRUB_GFXMODE=1200x800 save, then type sudo update-grub I tried vbeinfo and it says the preferred mode is 1366x768 which is the resolution I use.So is it safe to change the grub as suggested.Sorry I have never edited anything for grub and I am afraid to break somethings.Please tell me if it is safe so I can change the grub screen resolution.