Well,you said you "download files rencently".I am sure that is the reason caused your computer slow down.
Ok,in one sentence,you have confused your computer Regsitry.
Let me expalin:
Any time you make a change to any of your computers settings, through the control panel, they are stored and updated in the registry. So, how does the registry get messed up? Well, let’s say you install a new program, and it then changes one of the registry files to work with the new program. The new program works like a champ, but what about the other program. You don’t know yet, because you have not had to use it. But when the time comes to open the old program or run your computer normally, and the required registry file is not there, or is different, the computer might just sit there. It has no idea what to do. SO YOUR COMPUTER SLOW DOWN,SO THERE ARE A LOT OF ERRORS.These problems happen every day to people, even to me. And, this type of problem causes a slow or freezing computer.
Now you need to fix your registry files. And, I guarantee you have errors in the registry files that cause computer slow.Fixing these errors will dramatically increase the speed of your computer.Sometimes can up to 300% or more! All you need to do is run a registry repair software called registry cleaner, and get your Windows registry cleaned up and optimized. You will no longer have a slow computer.
You can check out http://www.computerspeed.info/index.php?t=speed1 ,there are reviews of top 5 registry cleaners and a clear guide to tell you how to speed up your computer.And from there you also can get a free scan to fix any problems such as computers slow,computer freezing, computer errors and getting the blue death screen.
Hope that can help you.