Check to see what's getting excessively hot while it's powered and running, fingertip touch to the tops of chips if you don't have an IR thermometer, be careful not to short anything.

Also check to see if everything is getting five volts that should be getting it, the bios chip pin 1, the DIP package 68000 CPU pins 14 & 49, etc.

Somes guesses are: a circuit trace has burned open from overvoltage, one of the processors (68000) could be damaged without tripping the watchdog reset/click of death, or the power rail has something wrong with it, check Q1 transistor, Q2, Q3, Q4, etc.