I tried to make the Windows option on GRUB boot menu the default by following the instructions I found on the internet. The instructions were good, graceful but since I encrypted the Windows partition after I installed Ubuntu, the graceful approach didn't work for me when I did update-grub. The option simply disappeared because decryption does not work under Ubuntu.
I found on the Internet some codes for grub.conf to restore Windows startup. It was successful but there is an error message after I select the Windows option.
I wonder whether update-grub automatically backs up a copy of grub.conf or any other config files it changes? If so, I can probably retrieve that config and get rid of the error message.
I didn't mean to encrypt, it's a company PC and encryption of Windows partition is mandatory. I do not want to decrypt the Windows partition, fix GRUB and encrypt again - it simply takes too much time.