QUESTION :
I have Windows 8 on my PC. Can I remove the Operating system without using any external disk or software. I’ve misplaced the Windows disk.
ANSWER :
You could do that on Linux, it would just happily keep on removing files until a big crash (something like this one). Windows, won’t let you delete components that are in use (i.e. crucial system files will be untouchable when it’s running).
But if you just want to disable it for some time, there are few things you could do.
Hardware solution: remove crucial piece of hardware, preferably hard drive: Windows won’t be accessible, actually nothing on the drive will be, computer won’t boot. To just prevent it from booting, you can simply unplug the power cord.
Software solution: make registry backup (not just export, backup entire C:WindowsSystem23config) and disable all system services (you’ll have to edit registry to do that, services.msc protects some services). When you want to bring it back to life, use some external tool to restore registry backup. (note that killing Windows with this method doesn’t require any additional tools, only restoring it does)
Currently there is no method to wipe a OS like windows 8 from within itself, you would need something such as Dban or a linux distro in order to wipe the drive completely.