I agree with Broni, a fresh installation of the operating system would be the best way to go. I will go one step further though, I would suggest using a program like Darik's Nuke and Boot
to overwrite the entire hdd. If there are any surprises on the hdd, this will remove them.
It has been suggested that you use CCleaner. This program has some useful tools, but among these is a registry cleaner. Because of the number of topics related to problems originating from the use of registry cleaners our staff doe not endorsed the use of them. The usefulness of cleaning the registry is highly overrated and can be dangerous. In most cases, using a cleaner to remove obsolete, invalid, and erroneous entries does not affect system performance but it can result in "unpredictable results". Unless you have a particular problem that requires a registry edit to correct it, I would suggest you leave the registry alone. Using registry cleaning tools unnecessarily
could lead to disastrous effects on your operating system such as preventing it from ever starting again
. For routine use, the benefits to your computer are negligible while the potential risks are great