I can't help you about factory reset, but I can give you some tips:
You can get a copy of Vista using Peer to peer files exchanges. Look for some Torrent sites. While it can tecicaly be called pirating, you only do it to repair your operating system. The downloaded OS should pick up your actual activation key and accept it without any problem.
That way, any saved files should be preserved.
Another option, if there are no files to preserve is to install any distribution of Linux, like Ubuntu, Gnome and many others.
You can get most Linux distributions absolutely free.
You can get the installers from the home site of those distros or get them via torrent downloads. The installers comes as ISO files to be burned on a CD. You then boot from that CD. You get to try before you install as you'll usualy get directly to the Linux desktop and have an "Install Linux" desktop icon that will actualy start the install process.