Using installed guest Windows as host system

[VseKupatsya]

I'm at funny case. I've 2 systems: Ubuntu and Windows (A), and Windows was not started up for about one year, but today it has been needed. Unfortunately, Windows A reboots every time I start it. The problem is that I have not CD-ROM and can't reinstall. There is another Windows (B) as guest OS under VirtualBox. Will system A work if I replace its files with Windows B's files?

[MarkCranness]

Have you upgraded VirtualBox in the last year?
Try setting IO APIC to on in the Windows (A) VM: Settings>System>Motherboard>'Enable IO APIC' checkbox : set to ON. I've heard other people say that a VirtualBox upgrade reset that setting.

[BillG]

If you can't get the vm to boot, you can reclaim data from it by mounting its virtual disk as a secondary on the vm which will boot.

[ahznb]

I'm assuming that Windows (A) is not booting from VB right? Copying files from (B) is not going to make your (A) boot. Try booting (A) in safe-mode and see what happens, you probably got a BSOD. Tell us what it says.