I'll throw in my 2 cents worth. The symptoms sound like a bad electrolytic capacitor, either at the power input of the board or in the on-board power supply if it has one. If these capacitors are bad, they can cause all kinds of problems. Sometimes they work, sometimes they don't. And if the power supplies in your computers put out slightly different voltages, the symptoms will be different or non-existent. They don't have to be bulging to be bad - that was big in the 90s when there was a bad batch out of the far east. The best way to check an electrolytic capacitor is with an ESR meter. Maybe you can borrow one from a friend or technician. Good luck.