How to clean pc?

I'm sellin my pc soon, so i wanna wipe everything off of it. only question is, how do i do this without having to uninstall the os.. as i dont have the disc with me.

Umm..

well. you could uninstall everything, delete all folder contents, etc then do a registry cleanup with CCleaner. After that run a program that cleans free space (aka permanently wipes the hard drives' free space preventing file recovery).

That being said nothing will leave the PC as clean as a reformat. if you have the key for your OS then you could borrow the appropriate disk from a friend or obtain the appropriate iso online. Then you could reinstall windows.

A program called Magic Jelly Bean will retrieve your Windows Product Key for you. I've used this before to retrieve keys on my computers. However, you will still need to find a disk, though any retail disk for your version of Windows will do.