After downloading/installing/running CCleaner my computer is running way slower than it already was. What to do? Uninstall and go to Norton$?

Did you clean/remove prefetch files? Were many files removed? If so, when was your last defrag? Norton? They make a cleaner?

You are comparing apples to pears

If you want any advice stano you are going to have to give information such as what operating system and service pack you have.

Did you install the yahoo toolbar?

Did you use the registry cleaner (issues) part of ccleaner?

What exactly is slow, browsing, opening files...what?

If all Norton malware protection has been replaced by CCleaner the computer's speed and response could be affected by malware.

Alan

Thanks for the attention!

Sounds as though you may have either some kind of software conflict going on or a virus/malware issue.

As the virus/malware issue is the most important one you should check it out first, it may be a good idea for you to follow the steps here

http://forum.piriform.com/index.php?showtopic=20120

If you come out all clean we could perhaps have a look at what software you have running especially security software, to see if there are any conflicts.