Ok so i'm a little computer illiterate so could someone please help me out.

I think somewhere along the way I think I must have accidently deleted something because when I click on System Preferences; in the applications folder, on the dock and in the apple menu, it doesn't do anything-no window comes up.
So I've been doing a little research to try and learn how to fix it.
One thing that I clicked on suggested that I copy the System Preferences file over from my external hardrive (where everything is backed up) onto the desktop then into the applications folder-all good. But instead of the problem being fixed when I try to open System Preferences a window pops up that says "You cannot use this version of the application System Preferences with this version of Mac OS X."

How do I get it working again?

I bought this computer 2nd hand so I don't have any discs or anything like that.

I'll love you forever if someone can help me out