sudo apt-get install gedit

fgrep menuentry /boot/grub/grub.cfg 

This lists all the bootable operating systems on your machine. Now copy the entry you want to be default which is in your case Windows 7 (loader) (on /dev/sda1). Note I have assumed it is the sda1 partition, if not please copy Windows 7 (loader) (on /dev/sda2). Copying in the terminal can be done by Shift+Ctrl+C.

Now, type:

sudo gedit /etc/default/grub

GRUB_DEFAULT='Windows 7 (loader) (on /dev/sda2)'

Close gedit and come back to the terminal and type:

sudo update-grub

That's it!




PART 2: (Optional Extra)

Hide the Grub2 menu, and use the default menu option.

Description: This both hides the startup menu, and shortens the (usually 10 second) timeout. The PC will auto-launch whatever the default option is on startup.

NOTE: The user just needs to hold down the Shift key (on startup), to again see the Grub2 menu.

STEPS:

D. Edit setup file

sudo gedit /etc/default/grub 

Uncomment the line '#GRUB_HIDDEN_TIMEOUT=0', to look like:

GRUB_HIDDEN_TIMEOUT=0

(Save the file and close.)
E. Update grub settings

sudo update-grub 

Now, on boot, you will AUTOMATICALLY boot to the default menu option, UNLESS you hold down the Shift-key at boot time. Then the grub2 menu will re-appear.