You could take your hard-drive out of your computer (if it's unbootable), Plug it in another computer, backup
all of your important files, Put the harddrive back in your "main computer", Reformat it, and then it should work.
You can either buy or download windows if you don't have a disc for it already.
And if your computer is built for a specific windows (Like XP for example) Get that.
Or else there is a risk that the drivers will lag.
And if you have 4 GB's of Ram memory or more, Get a 64bit windows
EDIT: Do not text that number, it's obviously fake. Why would microsoft put trojans/worms in your computer, Give messages in russian and stuff like that?