I've installed CCleaner and still my pc is very slow. Can anyone help?
There could be tons of other reasons why your computer is slow. CCleaner is not a guarantee to speed up your system if there are OTHER causes that are slowing it down. Could be a fragmented hard drive, virus, defective software, hardware damage or simply a dusty CPU.
Look into this article:
http://www.qozan.com/10-things-that-slow-down-your-computer/
Also it would help to give more info such as operating system used, what security software you have installed and any other problems you have noticed.