Have used: AVG, AVIRA, ADWARE, CCLEANER, CYBERDEFENDER, EUSING and others. But my comp is still slow. I think I might have downloaded something infected or downloaded some malware and I don't know how to get rid of it.

where can i find a registry cleaner that's free and safe because some freeware registry cleaner should backup first because they say cleaning can make dangerous changes on the system

My biggest concern is, I'm wary letting a program dig into my computer, I have no way of knowing if it's going to imbed spyware or virus or something on my system, or steal my information. I see pop-ups for cleaners all the time, but they don't come off as legitimate.

Registry cleaner? I have anti spy and malware software. Also, anti-virus software. I do disk cleanup often. Now I'm hearing that I need a registry cleaner. What's that?
Oh yeah, I also keep my browsing history completely cleared.
For instance, I'm able to do all the stuff this software claims to do without it…

http://www.ccleaner.com/
So, what's so special about it?
Is it just for people who don't know how to use their computer?

I just purchased a brand new expensive desktop.I would like to keep optimized for the best possible performance.There are a vast amount of registry cleaners out there all claiming to be the best,some I don't trust.What is the best way to optimize my PC,or are all those software programs actually no good at all?