Bugger. Powered the PC on tonight (I've been using it fine today) and...nothing. Lights come on but no POST or beeps then a few seconds later the power goes off and then switches back on - repeat until bored. Unplugged all the drives, took out the Gfx card and all but one stick of ram. Still the same. Reset the CMOS, still the same. Sooo, PSU, CPU or Motherboard?