Virtual Box Won't Accept .ISO To Install OS

Make sure that you are choosing the right OS under the settings. (eg. Microsoft Windows, Windows XP) If that is correct try choosing "Unknown Windows" for the version.

Otherwise it is probably a bad or broken iso. Try re-downloading if possible.

Oracle VM VirtualBox is a program that allows you to create operating systems on virtual machines, i.e. to use Windows programs on Linux. If a program doesn't work under WINE, for example, it will probably work in its native environment, Windows. Using VirtualBox would be a better and easier alternative than installing a separate partition for Windows on a Linux machine.¹

Once installed, just look at the images below on how to choose your ISO file. Once choosen, you ca go ahead and start the VM. If the ISO is bad, or there is something wrong with it, you might want to verify it, by doing an MD5SUM for Linux. and MD5SUM for Windows, otherwise, just download it again.

You can use an ISO file, or if you have burned the ISO to CD, choose Live CD/DVD.

Now when it comes to Windows, I have had some issues, when the ISO is not downloaded directly from Microsoft. And just follow the guide below for step-by-step.

¹This WikiHow page has a complete step-by-step on how to do it.