I have the exact same problem, except my Kindle is wonky after the font hack was installed. I followed the jailbreaking instructions exactly, and all was fine. Then I followed the font hack instructions, and though the menus weren't working, I did the blank "boot" file thing and it was okay. Then I add the Arial Rounded Narrow font, and everything went to hell. Nothing worked right, when I tried to select books it told me that none of them were available. At this point I figured my best option was just uninstalling the font hack so I put the right uninstall file at the root, and did a hard reboot (because I still can't access the Settings screen).
When I hard rebooted, I get this screen.
So I'm stuck now. I can get back to the regular Kindle home screen, but I basically have a half-broken Kindle, which I assume Amazon won't be too happy to deal with. Any suggestions?