As I have to look after a Windows computer (these are my sins for having once done it professionally, oh so very long ago...), I found myself having to go and find a registry cleaner.
Here's a tip for you: If it says "Free download!" or "Free scan!", pray that one day you get to meet the company, so you can punch them in the face.
Yes, you can download for free, and you can scan for free and be told that you have 750 errors, but you can't actually do anything about any of them until you pay to register it.
I recommend, if you feel you need a good registry checker, Glarysoft Registry Repair. I have no idea how many other actually free ones are available, but that was the first one I found, and it seemed to actually do something.
It didn't actually fix my problem, which was Nokia Map Loader not running due to an Msvcr80.dll error, but unlike any of the ones I had to download and install before I found out that they were ass-bandits who expected me to shell out money only after running a scan, it was incredibly non-annoying.