I have an iMac and I dual boot Windows and OSX. Last time I boot into Windows from OSX which is quite easy. Now I can't seem to show the option to choose which OS I want to boot. I have a non apple keyboard. I remember holding option key should bring a page up during booting to let me choose. I have tried with my win key and alt key. None of them seem to work. I have searched on the internet. People say it should work. But I don't know why mine doesn't work.
While not addressing your ALT (option) while booting issue (for this you should provide a youtube video of what you're doing), you can still boot back into MacOS if you install Apple's BootCamp Control Panel software within Windows. This will allow you to select MacOS as the next boot.