If it's still slow after you did a reset or refresh of Windows, it's a hardware issue. Otherwise it's solved.
Read http://www.howtogeek.com/132428/everything-you-need-to-know-about-refreshing-and-resetting-your-windows-8-pc/ before you delete things you wouldn't want to delete.
i have a vary critical speed reduction problem on my computer , my computer is working too slow for almost tow weeks now , at first i thought it must be a virus , so i installed an eset nod 32 updated anti virus and i full scanned my PC and it didn't work , then i de fragment all of my local disks and that didn't work either , i thought it might be a hard drive problem because every time i opened my task manager , my disk processes shows 85% to 100% while i'm not doing anything , so i scanned for bad sectors and found 8 and repaired them, so far no difference , my computer still working pretty slowly!! please , if anyone has a solution i would be grateful to know about!!