Obvious thing is to open up task manager and look for things eating up cpu time. You may have to customize the displayed columns for a better idea. Next look at startup programs (startup tab in win8's task manager). If you're using a prebuilt system that you never installed fresh on, it probably has shitware in the background. You'll need to uninstall or prevent it from loading at start. After that, go through your installed programs list and uninstall things you don't recognize.
Generally CCleaner can do a lot more harm than good when run with no clue, especially if you let it clean your registry (don't, really don't), but it can find junk for you to get rid of. Can also try Adwcleaner
https://toolslib.net/downloads/viewd.../1-adwcleaner/ but really, you should go through your system yourself since any of these 'cleaners,' especially ones that can 'clean' your registry, can potentially bork your system.
edit: don't forget the couple links right here on these forums:
http://www.bluegartr.com/threads/782...es-and-Malware
http://www.bluegartr.com/threads/552...-and-Utilities
Old posts but the info isn't that outdated.