After the windows installation finish, add some driver, installing some apps for day to day work like office suite, browser, image editor etc your computer was perfect. Fast and responsive. But when time goes on your install more app, uninstall some apps, browsing and working with lots of files your computer became slow and unresponsive. Before this happen you have to Clean Registry routinely right after installing windows.
There're lots of Registry Cleaner out there but RegWork is the best one, and did I mention that it also free?
Registry Editor. You'll have it right when you need to edit some key on your registry.