Do you feel a "laziness" of your computer when you browse on internet? Maybe you got a spyware or virus. I check this kind of problems using a Live CD: a cd with Linux, you boot from cd and voila! You have an alternative operating system not affected by a virus/spyware, and you don't change anything at all on your computer. When you boot "normally", from harddisk, you have your good old Windows - I don't think you play games from Linux.
Also, it depends on your network performances. How good is ping response from your computer to your gateway?
Where did you "pinged", to what destination? In your local area network? It is a very very bad result if you receive a response after 500 milliseconds from a computer in your lan. To another computer/server on internet, not on your lan? Than it is a so-so response, but yes, you won't be able to play anything but board/card games with that latency...