What grade are you in? Chances are you're higher up than I am, but maybe I can help. I average between an overall A and B from time to time...
That really sucks, I guess it's karma.
My advice: No offense, but be more mature about it. The petition will not convince your dad, nor will wining. Ask your teachers if there's any possible extra credit work to do, and isolate yourself from your computer. Don't go near it, just study. Take all of your seriously, effectively use your time in school and try to get your work done. Hopefully then your dad will realize you're trying, but one problem: He'll either A) Not notice all of your effort and barely consider lifting the punishment, or B) You'll have to resort to making it somewhat obvious to him you're trying, and he might think you're sucking up and think you're not really trying (ironic though how what you really are trying, just not at grades, but rather convincing him something). I don't know how he'll react, I don't know your dad, I'm just predicting it based off of knowledge i DO know.
Good luck soldier. *solutes*
