New Lenovo Z70 running slowly?

About a week or two ago I bought a Lenovo Z70 laptop. It has an intel I7 core and 16gb of ram. Recently (the past few days) it has actually been seeming pretty slow performing basic tasks, like opening a video or audio file. Seeing as it's a newish computer with a relatively clean hard drive, a good core, and plenty of ram this surprised me when it started happening. I do download a lot of stuff off of the internet, so I was thinking maybe I got a virus of some kind ( even though I do have an antivirus program). Does anyone have suggestions on how I could clean up/speed up my computer?

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