I would do a clean uninstall of your client and reinstall it fresh. It might be something that got downloaded unintentionally or some other program interfering with your game. Also, play on your alt account for like a month, even after your other one is up if you can, and see if it happens again. At least that way you will insure that your main account won't get premabanned for something you aren't doing.
Edit: Also, there has been some speculation that if you are in a game with someone who is hacking on your team, your account is at risk for the ban too, which is stupid if it is real, but also a lame possibility.