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