Steps for entering/running the single user mode.
1) Reboot the machine. At GRUB [Boot Loader] there will be the listing of the Kernel selection. You will only have about 2 seconds to catch this option during the boot process. You will need to push the Esc key, F1 or Del key to enter this mode. (Depends on the server OS)
2) Select the version of the kernel that you wish to boot and type e for edit. (you may have more that one kernel version to choose from. The latest kernel should work fine) A list of items in the configuration file for the Kernel you just selected will show up.
3) Select the line that starts with kernel and type e to edit the line.
4) At the end of this line, hit the Space bar and the type-in 1 Press [Enter] to exit edit mode.
5) Once back at the GRUB screen, type b to boot into single user mode.
Once there, you can make root level changes like resetting the root password, modifying the xorg.conf and other things.