If you have dual-boot as me, Ubuntu and Windows 7, and wish to have Windows 7 as default boot.
Edit /etc/default/grub file, and change the value below to the line of your Windows 7.
For example, my Windows 7 was at line 5, you need to put it as "4", as the numbering starts at 0.
Save and exit, remember to run below to make it effective.
Now reboot and it should have Windows 7 selected by default.