Phono Stage Cuts Out

Total guess, but if just turning the power off and allowing the capacitors to discharge settles the problem, it could be a capacitor. Since it is not effecting anything else that should at least limit it to the phono circuit. If you have a voltmeter and a schematic you should be able to figure out what voltages go where.
My son had a similiar effect in a sunfire preamp, it would not let him change venues(CD, phono, etc.), till he followed your example. He decided to let it go to a friend who is an electronic tech and could take care of it. Never learned what was wrong.

If it goes dead silent in one or both channels with no other signs of trouble, it's likely to be a relay that is malfunctioning. Not likely to be a capacitor problem. This fact is not a lot of help to you, because you will need to have a knowledgable tech fix it.

Thanks alot for your responses. It's interesting or perhaps simply coincidence that this issue started when I changed from the stock power cord to a very expensive Virtual Dynamic PC.