Q. Is there a fix for the clock loop in the fonts exploit?
A. No. At the moment there isn't. Some Xboxes never see the problem, while others see it quite often. A general rule of thumb: If you decide to use the fonts exploit, never unplug your Xbox. You should also make sure you use an updated font (B&E reloaded, Bigfonts, or Mechinstaller Fonts). If you must take it someplace, the Audio Exploit would probably be a better choice. There ARE three things you can do if you do get stuck in a clock loop:
1) Try connecting a network cable to your hub/router/modem and letting it loop (You could also put in a scratched music cd)
2) Hotswap
3) Wait
Again, these aren't fixes. Even though the hotswap will remove the problem and allow you to set the clock, it isn't a wise choice for a fix (as it's tedious and risky).