"Pool88" gave you bad advice, unfortunately: "download the ccleaner and run the registry fix that might help." However, it is possible you "lucked out" and no harm was done. Below is a lengthy discourse by knowledgeable people on another site telling that Registry "cleaners" accomplish nothing and ofter cause harm. Furthermore, see the "sticky" at the top of the posts!
Advice and Info re Registry 'cleaners'
The main reason they are apt to cause problems is because the cleaners do NOT just clean up stuff left over from uninstalls. They also "guess" that other items need to be deleted, many times incorrectly. They also attempt to "fix" references to files that no longer exist.
As a result, you can end up with programs that no longer work, functions that no longer work and in some cases a PC that will no longer boot.
There is no performance gains to be had by running these things. Windows does not read the entire registry when it is looking for something. It uses the keys which allow them to go straight to the item that they are looking for.
If you really want to see how active the registry is in your normal running environment, download and run Regmon.
As you will see, the registry is constantly being accessed. If, for each of these, the entire file was being searched, your PC would be amazingly slow and not responsive.