Incase you run Linux and you come across this error like No screen found , then you would need to edit your xorg.conf . Fortunately there is an easier way by just answering a few questions.This error is noticed, when your linux machine's GUI doesnt load up.Instead you are faced with a terminal sort of screen, which is indeed the terminal after you login.Then once you type startx you see the error NO screen Found.Well there could be many reasons , Either something went wrong with the xorg.conf or you may have installed a new Graphics Card etc etc ..Incase you have installed a new graphics card, then there's nothing to worry as it is a common thing, once you edit the xorg.conf and tell it that you have THIS video card then everything would be sorted out.So here's how you do it :

Step 1 : Boot your Linux machine
Step 2 : Grub would start loading the linux distro
Step 3 : Then you are faced with the command line which asks for your username
Step 4 : Then enter your system username and password
Step 5 : Then Type startx .If this works, and doesnt give any error, then everything's fine , you dont need to edit xorg.conf .If the GUI still doesnt load, follow the next step ( step 6 )
Step 6 : Then type sudo dpkg-reconfigure xserver-xorg
Step 7 : Allow the setup to automatically recognize your card, leave most of the other settings to default.
Step 8 : Once done with that , you should be brought back to the command line
Step 9 : Now, just type startx
Step 10 : Your, GUI should load now , without any trouble!!!