its just dos, or you use windows too?
check it out
If by MS DOS you man the Command Prompt that appears on your Repair option on teh XP CD or when the system is running under its own steam, at the prompt, type %systemroot%windowssystem32rstrui.exe and hit Enter.
found this one too, see if it works
You want to reformat your hard drive or just replace it with a new one. You will need to re-install Windows. Just so you know, you will lose everything you had saved on there.
get back to normal
Quite often you can press and hold function key F11 or perhaps F12 at power on? I'm not aware of any cmd shell commands.
Stay away from ms dos when you do not know what you do. Download Linux (www.ubuntu.com) and forget windows. Only cost you money.