Good chips in bad sockets still look like bad chips. Pull the CPU and Rom chips and examine each pin well with a magnifying glass. Look for wide, loose sockets and contamination and corrosion, even dust. Carefully look over the side expansion connector. Check for solder bridges and ensure the bottom shielding is not shorting anything. Look at ALL the sockets, even with the square chips installed, for irregular pins.
If you have a multimeter, check the power supply rails on the motherboard (not the power supply connector).
