You do not need to post to keep your account active, all you need to do is login to the Forums at least once every two weeks.
If you are suspended for Inactivity you should be able to unsuspend yourself by going to your site, Clicking the "check suspension reason" button, typing your cPanel username into the box, then clicking "check suspension reason" again. You should then see the reason why you are suspended and a button to unsuspend yourself.