I installed parabola GNU/Linux alongside windows 7 recently. After a reboot, I couldn’t see the Windows entry. I did install os-prober before installing grub.
Then I figured there must be something wrong with the grub installation, so I reinstalled grub, but still no luck.
OK, I know you don’t really enjoy the story, you’re here for the solution, I just want you to make sure that your situation is quite similar to mine. And here the answer is:
1, mount the partition where Windows exists.
2, run os-prober, if you didn’t install it, now is the time. It should detect you windows now.
3, reinstall grub or regenerate grub configuration file.
There you go, you have your windows entry back.
The point is, you have to mount the partition first for os-prober to detect your windows.