Hello,

My OptiPlex 780 won't turn on/boot. When the power button is pressed nothing happens but if the power button is held the number 3 stays lit until I let go of the button.

When it it plugged in and the switch turned on and before any buttons are pressed the numbers 1 and 3 flash on very quickly before going out and this repeats. There is also a yellow light which stays lit on the motherboard.

There is no beeping whatsoever and no video output at all. The only things plugged into the computer are the power cable and sometimes the VGA cable to see if there is any video output.

If the power button on the back is pressed, it lights up green and the fans start whirring but there is still no video output. During this, the front power light is a steady amber and the flashing 1 and 3 go out.

I have tried unplugging and plugging in the cables inside, I've removed the RAM and replaced it to no avail and I've reseated the CPU. I've also tried using a different power cable.

Any and all help is greatly appreciated.