I had a similar problem with the font hack - the first time I just used the "restore to factory setting" and all went back to normal, the second time I was even unable to access that menu item but I was able to use recovery mode to get it all back to factory state, I did not try a third time :-)
Here's how:
http://blog.laptopmag.com/kindle-cri...#axzz16DtMZd2G
My problem was that after the hacks the menu items did not work properly anymore and then it would boot to a blank screen - dunno what the reason was, but I hacked my Sony 500, my 505, and my PocketPro all without problems and will continue to use hacks, after all, I always learn from my mistakes and most of the time hacks work just fine and I am simply in awe of the people who come up with them, they do such outstanding work!