If you've boughten Photoshop, then you have a disc somewhere. Just uninstall Photoshop, and then re-install, problem solved.
If you bought it online from Adobe's store, contact their customer support, give them your transaction number or whatever to prove you bought it from them, then they will either give you files to download to fix it, or send you a PS disc.
And if you didn't buy it, then go do it. Don't be stealing somebody else's hard work.