Sounds like dead bridge rectifier(s) on the PSU, probably on 5V at least. There's not too much else I can think of that would cause this. If I had that machine here, first thing I'd do is unplug everything from the PSU outputs to prevent further damage, and check the outputs. It'd be nice to do it with an oscilloscope, but just a voltmeter would be enough to tell you whether 5V and other outputs are sensible.