help with Ack Dack problem

It seems my new Ack Dack has developed a problem, ill try to explain the symptoms as best I can...
when i went to listen today i turned everything on as usual and...nothing, no music...so i turned off the dac for a few mintues, turned it back on, and music would play but a static popping sound was coming through the speakers...this grew in volume and them the dac went dead again...i repeated this a number of times with the same result...with music playing a static poping sound would grow in volume over the sound of the music and then the dac; would die in a squelching not very pretty tone.
in trying to figure out the problem i noticed some other symptoms...with the dack and transport on but no music playing there is a constant hum coming from the speakers which can be turned up and down with the preamps volume control...however if the volume on the preamp is left alone this hum again slowly gets louder...like feedback on a guitar amp...
if i turn the transport off but leave the dack on, the hum becomes lower pitched but otherwise exhibits the same properties...
the hum is there with the digital cable disconnected and with the transport completely unplugged, i also tried a different pair of analogue interconnects thinking they might be picking up some interferance but it persists, i also unplugged everything i could think of, like tv cable box etc thinking something might be interfering but no help...the dack is only a couple weeks old and has worked fine till now

please help!!

mike