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An operating system wasnt found
VM was suddenly aborted, when trying to start the virtual machine the system is unable to start


An operating system wasn't found. Try disconnecting any drivers that don't
contain an operating system.
Press Ctrk+Alt+ Del to restart

I have tried to do the following without success:

1. Adding Windows.iso withing Devices -> Optical Drivers -> Windows.iso and trying to perform a repair
2. Enabling EFI within Settings -> System -> Mark enable EFI

Do you know if there is a solution for this.

Based on a web-search on "An operating system wasn't found. Try disconnecting any drives" this is a Windows error that appears in a Windows OS where the boot loader cannot find an OS to boot to.

In order for Windows to produce this error the Virtualbox VM has to be running correctly.

Since the problem is within Windows, you should web-search how to fix it inside the VM's OS from Microsoft help channels. Such as this: https://support.microsoft.com/en-us/top ... 6f3888906b

Regarding the VM suddenly aborting, what caused this? Did you get a Guru Meditation? If so, post the VM log that contains the Guru Meditation. (You can find the log by right-clicking the VM in the list and choose Show Log, then search each log for "guru meditation".