For $400, you can not get a brand new "gaming" laptop for just about $400.
You can get a used one, from Craiglist, but even then you'll be hard-pressed.
I'm not discouraging you, but, as someone who had recently bought a new laptop, with tons of research, I wouldn't bank on it.
Check out Lenovo, but stay away from HP, Dell, Alienware (you won't be able to afford this one anyways).
For $400, APU might be your best bet, but check out the graphic card of the laptop you are purchasing as to how it does for the game you are playing.
I play SC2, so I was checking benchmarks for SC2 to whatever laptop I was choosing, I advise doing the same, so there are no surprises at the end.