I'll try taking out the memory and reseating that too, it's got 8MB (4megawords) I think on a single board. So far all I've done is replace the back light. Bit stumped by this dodgy fx problem, I wonder if it's some kind of corrupted memory address and if so where it's getting corrupted (bad EEPROM? - but wouldn't an OS loaded off the disk overwrite the OS in the CPU's RAM anyway).
Will keep you informed.