Windows 7 Home Premium 64 bit, computer works fine if booted up when cold. It will also restart (soft boot) without a problem but if I shut it down, it will not boot until I leave it off for a long time - overnight always works. I have replaced the power supply with a brand new one and replaced the BIOS battery. These changes made no change in the way it behaves. When it refuses to boot there are no BIOS beeps all fans and lights work except the power light. The power light works fine when it boots when cold and when restarted.