HP Z620 Workstation, 2x E5-2643 Quad Core 3.3Ghz with 64GB, 512GB SSD, GeForce GTX-670 video, Windows 10.
It has been running perfectly, but I found it had powered off overnight on its own.
When I press the power button, there is only a quiet, rapid ticking from the speaker, no POST, no beeps, no video, no HDD activity light, all fans are turning slowly, steady blue LED on the motherboard, steady green LED on the power supply. After 60 seconds all the fans run up to full speed, very loud, but there is still no video.
The keyboard LEDS flash once at power-on, but not when NUM LOCK or CAPS LOCK are pressed.
The DVD drive tray opens when the button is pressed.
1. I removed the 2nd CPU riser and powered on, this time NO ticking, but still no POST, no video, after 60 seconds the fans take off.
2. I swapped the video card for a different, known, good card, same result, with and without riser. (The Z620 has no onboard video).
3. I removed all USB devices and used a keyboard and mouse with PS/2 connectors: same result (CAPS LOCK and NUM LOCK LEDs flash at power on, but do not light).
4. I removed two 4TB Seagate drives and left only the original SSD C: drive in place, same result.
What could have happened? How do I troubleshoot this condition?
Thanks,