it sounds like your parents hate video games altogether for the wrong reasons (violence), but it could really be that they are just looking out for you in a realistic manner and they're just making violence an excuse, where they want you to have other interests than video games (not sure if you do). if you don't have other interests and do get your own computer, they are very likely right in that you'll waste a lot of time in your life
in the case that they don't want you to play video games because of violence and that is the only reason, you should probably try to educate them why it's really not that big of a deal, first by yourself, then from another adult, such as a counselor or something. probably won't do much, so marxist/raytek's advice is pretty solid.
in any case, it seems your parents want whats best for you and probably love you lol, in which case you shouldn't do anything that you'd regret a few years down the road, such as completely removing them from your life.