I'm looking for a $ 500-600 gaming PC. Any suggestions?

So I'm a PC noob. I've always been a console gamer until a few years ago. I joined steam to play free to play games, and eventually bought games like Garry's mod, counter strike, arma 3, natural selection, etc. I checked the specks for my laptop which is toshiba and my family hp desktop. Both can barely run Garry's mod and counter strike. I'm looking to buy one in the near future. I've heard about steam boxes, but don't know much about them and don't know if i should purchase one in the future. If anyone can list some good gaming pc's that can play games like arma, minecraft, Garry's mod, etc and are at a good budget for a working teen, I'd appreciate it tons.