anniesboy, Registry cleaners are little more than "snake oil". Your Registry doesn't need cleaning, and because it's so important to the running of Windows, if just one tiny key is deleted it can render the computer unbootable.
Don't waste your time with them because they won't make your computer run any better or faster and there's always the risk that serious damage can result. Folks who understand how computers work would never use such a tool on a regular basis.
If however you have a specific problem then very occasionally they can be useful.