First, I upvoted the post for the thread title, not what happened.
Anyway, I've never used those cleanup sites and don't trust them. I would suggest you find a free antivirus scanner (all of the computers at my house have avast, but your preference is likely different (I've also heard good things about superantispyware) and malware scanner (malwarebytes is the most popular I'm pretty sure). If neither of them do anything, you could do a system restore to a few days ago. Registry Mechanic is another random program that doesn't deal with malicious software, but cleans up your computer and can greatly increase your computer's agility.
Also, remember that computers age just like everything else and get slower to. I would say that was the problem if it wasn't sudden.