Thank you very much! As you suggested, typing c at the grub menu, followed by set root=(hdo,msdos1) chainloader +1 boot took me to Windows. I suspect that there must be a way to fix my grub menu, but don't know how. The output from os-prober: /dev/sda1:Windows Recovery Environment (loader):Windows:chain /dev/sda2:Windows 7 (loader):Windows1:chain /dev/sda3:Windows Recovery Environment (loader):Windows2:chain