Windows & Ubuntu dual boot.No menu to choose OS?

According to Ubuntu documentation, you should be able to see boot menu by pressing any key. Try also pressing shift early in the boot.

IF that doesn't work, try editing /etc/default/grub . If you want to edit it in gedit, run this command at terminal and enter your password:

gksu gedit /etc/default/grub &

You should see line like this:

GRUB_HIDDEN_TIMEOUT=0

Now remove the zero from the end:

GRUB_HIDDEN_TIMEOUT=

According to documentation, this should cause GRUB to be visible every time you boot.

Now save the file and update grub with following command:

sudo update-grub

If everything went correctly, you should now see GRUB2 (boot menu) every time you boot.