If you want to use only windows, and quit using Ubuntu, why not start
up Ubuntu from the cd?

You can then work on the grub and make windows the default OS. Then
change the display time on grub and you won't know there ever was an
option for another OS. Simply said, windows will start up without any
screen just like it did before you tried Ubuntu. You will not need a
password because you will be starting from the CD. And yes you will be
able to read and write to the grub files no problem.