Slowing problems can be hard to find sometimes, they can be related to adware &/or malware, overheating, file &/or driver corruption, or just need to run Check Disk & Defrag.
System Idle Processes are the amount of resources available for use.
Open the case and see if the is an excessive amount of dust buildup on the fans, of course shut down the computer first. Start the computer with the case open & make sure all the fans are running at what looks like normal speed.
See this article:Taking out the Trash
Show all Files & Foldershttp://www.bleepingcomputer.com/forums/ind...showtutorial=62
Try these free tools.
Trendmicro (free virus scan only)http://housecall.trendmicro.com/
Adware SE (update after installing)http://www.lavasoftusa.com/software/adaware/
Spybot S&D (update after installing)http://www.download.com/Spybot-Search-Dest...4-10122137.html
Let us know your progress.