My PC games like fifa 11, nba 2k11, assassin's creed start lagging today. It only started lagging after the match started (no lagging before menu screen) . It is not my pc spec that cause the lagging because I played these games for a whole month without lagging. I also noticed that my computer is a little bit slower than usual. I think the last thing I did is my assassin's creed crash and i pressed the power off button. The first around 8 times I played it, it didn't crash but after that it always crashes after 30-40 minutes i play. So I don't know what to do and press power off button, then wait for a while then press on again. And there is some new problem occur. When I'm watching video using chrome, sometimes it lag or just got no sound when the video is playing. Is it because of the graphic card or virus? I already scan with avira, malwarebyte and spybot. There is no virus according to them.
My pc specs are asus n53s, intel i5, 4gb ram, 640hdd, window 7 and nvidia geforce gt540m 1gb.