I'm surprised that no one mentioned Malware/Virus, etc...
Slowness of one's PC, Mac, etc.. can contribute from Malware that bogs down a system. Use MalwareByte to check that you don't have any sort of Malware infected programs or bug in your Root Directory. http://download.cnet.com/Malwarebytes-A ... 04572.html
Also, perform a Flushdns in your Command line prompt:
Start > Run > type: "cmd" (w/o quotes) > ipconfig /flushdns
Turn off your Router, wait 10 seconds and turn it back on... (This is a network refresh, in case the speed of your network is slow).
Remember, CCleaner does not get everything out for you, you will need to locate other garbage and redundant data left in your AppData that CCleaner don't get on default settings.
You have the ability to use the AUTO function in CCleaner file, to let it do it automatically. But you can set it manually in the option, to automatically run after it has been rebooted, etc...
You should also use RevoUninstaller's Free version to remove redundant leftover files.
You should always check your root directory to see any odd looking file names that may appear suspicious, which may be contributed to malware and infection that slowed your system.
Just a few thoughts....