One other thing now I look at a downloaded copy of the motherboard photo.
It looks like some liquid ingress on the side where those dip switches are.
Write down the current dipswitch positions, then flip them a few times to help clean the contacts.
You could also try spraying some deoxit into the switchs before toggling them a few times then
give it some time for the deoxit residue to dry and see what happens.
Depends on how much time you want to spend in it..
I have fixed strange problems with old boards by giving them a good rinse and clean, then allow a couple of days for the MB to dry in warm weather. Also measure the power supply outputs, even try using a replacement supply with AT power connectors to see if that boots. Always use a soft brush to clean boards, preferably at a static safe workbench.
Hint, when you think the board is dry, use an air blower to check that no water comes out from under the surface mount chips.
