Over time "crap" accumulates in the background that windows generates then has to keep up with. If left, it can seriously slow down even a hotrod lap or desk system. Some housekeeping is done by windows but in some cases, it just makes it worse.
A lot of us here used these programs to keep our systems clean and happy.
PC Cleanup Toolbox
I'd advise staying away from BlackViper for now. Some of the suggested settings are for advanced users and may do more harm than good if you don't know what you're doing.
Oh and run a deep virus scan.