Keyboard Ghosting (A & S + ↓ or ←)

​I have an alienware 17, 2014. I've had it for so long but I just noticed I can't press the A and S keys plus down or left arrow at the same time. I can however press the A and S keys and up or right arrow at the same time, or any other keys for that matter. I just wanted to know if this was normal, I don't know why I only noticed now.​

​it also sticks, when I am pressing say A,S,↑ then press ← and release ↑ it still registers that I'm pressing ↑. If that's the way it is then that's fine I just don't know why I never noticed after all the games I've played.​

​In any other case I can press 5 or whatever more keys at once, it is just A & S + ↓ or ← keys that cause the problem.​