@clivesson
I think it may be that there is some sort of Metal Particle stuck in between 2 chips or causing 2 contacts to touch. make sure you take some sort of vacuum or brush and clean the circuit board, even removing the sheilding and floppy. Also try booting without the mouse or joystick connected as well as thee RGB monitor......usa a TV instead.
Hope that turns out to be the problem and you solve it.
