It is probably, as the others write here, bad contact in one or more cards. I have had the same problem several times with G68 devices.
After I cleaned the contact on the cards, it worked.

It is also important to clean the connectors on the backplane. I use a spray can of oxide clean for that.

When you insert the cards, I recommend that you insert and remove them several times.
To clean the contact surface of the cards, I use an eraser that is suitable for the purpose.

Has the G68 been subjected to a power supply failure? If this is the case, it may damage some of the cards as well.

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