Have you read any links at http://www.google.com/search?hl=en&q=Firefox+won%27t+start ?
I click on the Firfox shortcut on the desktop and an hourglass shows up for a few seconds and then nothing. SSC firewall asked at one point if Firefox could connect to the Internet; I clicked Yes. I went into Program Files\Firefox.exe...nothing. I uninstalled Firefox. I reinstalled Firefox, and it seemed to work once. It just won't fire up now.
What could be going on here?