If it sometimes asks you for the root password you can't be root.
Try this:
Open a terminal (Click on the Applications menu, select System tools, then select Terminal)
Type:
enter the root password (if it asks for it).
Type:
Code:
gedit /boot/grub/grub.conf
A screen editor window should open. Find the line
Change the 5 to 1000 or whatever you want. Save the file.