Last couple of days when I’m turning on my computer, there’s a window where I can choose operating system (Windows 8.1) or “Undo Compression”.
I have no idea what is this and why am I seeing this. Any idea?
This seems to be a pre-boot options menu. It appears most likely either because you have an installation media such as a USB drive with Windows 10 on it plugged in or a DVD in the optical drive, and the computer is set up to load from them first. It should not appear if you take them out before starting up.
Or it could be because you have done a compression and this got added as an additional boot option. In this case you can remove it after booting into Windows and pressing WinKey(to the right of the left Ctrl)+R, and typing in
msconfig. That should open a window like this:
In your case there would be an extra option like “Undo compression” which you could should be able to remove.
I haven’t had that exact situation happen to me, and so this might not be 100% correct, so please comment to explain what is different in your case from what I’m supposing is happening, as it might be helpful info for everybody else who encounters the same issue.