I have used registry cleaner/repair in the past, but in my opinion they don't achieve a lot. And you need to be sure you've got one from a reputable source.
A very good reason to ensure you are getting the O/S disks when you buy a PC, and to backup your data so it doesn't get lost. Then, when things don't seem quite right, getting slow perhaps, or warning of errors, you can wipe the hard drive and install from scratch.
PS I think CCleaner is one of the better PC cleaners. But check the settings or you may lose history or remembered usernames etc. that you weren't expecting to be wiped.