Ok, are you root when you try to access the file, you need to be, what distro are you using, what file editor do you use (eg gedit)
this is how you get into the Xorg: sudo gedit /etc/X11/xorg.conf
if not in Ubuntu just type su as oppose to sudo and & if you don't use gedit try another file editor like Vim.
or just go to the Run feature in your menu and type /etc/X11/xorg.conf that will open the folder then click the icon called Xorg.conf
hope this Helps,
Jake
EDIT: reply posted whilst typing