Why is my PC running slow?

Recently my gaming pc made a lot of noise everytime I used it and I don't know why, but it did it for about a week and after it stopped making the noise my pc started lagging really badly. It normally runs games on high graphics at good fps rates but not anymore, and it even logs using just...

My USB stick had movies and loads of music on it. One day I put it in the tv and the kids had somehow over-ridden the music folder. I put it in the laptop to see what happened and there were no files on it. I checked the storage availability and I had nearly none. So the files are there...