My Mozilla Firefox won't start. help me with this problem please!?

I've been trying to fix it all day. no luck. my last resort was to post this. I've uninstalled and reinstalled Mozilla Firefox. it still doesn't start, even in the end of the installment it was suppose to launch. it was fine yesterday, have no idea what could have caused it to not start. if someone has had the same problem and got it fixed- please help me! or knows someone with experience on how to fix the problem, much appriciated to you! i only use Firefox with my homework... and everything! Firefox is so cool! cause Internet Explorer is kinda slow on my computer. like right now- as im typing. PLEASE HELP!!! thank-you :)