A few weeks ago my pc started acting weird all of a sudden. I was playing a game when it started lagging as all hell, so I tried to close it. Then it turned out it was my whole pc was incredibly slow , so slow it takes over 5 minutes to switch between windows. And since then it starts acting this way after only 20 minutes. I have windows 8.1, 4GB RAM and a 2.61 GHz processor. Does anyone know how it's caused?