As mentioned earlier, this problem occurs when your ISO file is corrupted, or the ISO file is not attached to the virtual machine. While creating the virtual hard disk, users need to select the ISO file. Otherwise, they can face this issue.
FATAL: No bootable medium found! System halted
To fix this problem, you need to go through these steps- Before getting started, make sure you have a valid and non-corrupt Windows ISO. After that, follow these following steps to get it done. Open the VirtualBox software in your computer, select the virtual machine, and click the Settings button. Alternatively, you can right-click on the virtual machine and select Settings from the context menu. After opening the Settings panel, go to the Storage section. Here you have to create a Controller: IDE. For that, click the Adds new storage controller icon and select Add IDE Controller.
Next, click the Adds optical drive icon and select Choose disk button. Here you can find all the attached and non-attached ISO files. However, you need to add the new ISO file that you downloaded. For that, click the Add button and select the ISO file.
Now, select the .iso file from Non Attached section, and click the Choose button. After that, make a checkmark in the Live CD/DVD checkbox, and select IDE Primary Master from the Optical Drive drop-down menu. After saving this change, try to boot your virtual machine. You should not face this problem anymore.