Well, the messiness depends on whether or not you can get into the bootloader. I think there are three options:
a) the board has an electrical problem (e.g. a short, or something burned out) in which case you'd need to figure out which component is dead and replace it (this is the worst-case scenario, and if the board worked fine before and it's well designed, it is very unlikely).
b) the board is OK, but there is a problem with the firmware:
1) even the bootloader doesn't work (i.e. pressing esc when powering up via USB does not bring up the bootloadHID device). Not so good, you'd need to flash a bootloader using and AVR ISP programmer (another device).
2) the bootloader works - this is the best case scenario - just flash it again with HIDBootFlash, maybe try older firmware...