So I've pulled the motherboard from the case and still same problem. Fans seem to work and the green light goes on (the motherboard) when I swith on the I/O switch at back of psu. No burned capacitors or visible signs of wear that I can see. Still a mystery...it's an Asus PB5 ATX775, can't find any info on whether or not this particular MB has an internal speaker and there's no mention of it in the manual. It's dead silent when I fire it up with no RAM so maybe that's a telling sign