Help with computer dianosis (No display at all)

corvo_1

Prominent
Jun 8, 2017
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Posting this for a friend, but here's the situation:
At some point today, his computer gave out and no longer displayed anything on the screen. He's tried re-seating all of the components and he thinks it might be either the CPU or the boot drive which has died. Unfortunately, there is literally no display so he can't even get into the BIOS to see if the boot drive is listed there. He tried using the onboard graphics with his Intel CPU and he still didn't get a display which made him rule out the graphics card as the cause.
He says that when he turns the system on, it stays in a restarting cycle as if it's trying to boot, but can't.
What sort of further diagnostic procedures should I tell him to carry out to narrow down what exactly is wrong?
(Only tagged as storage as he thinks it's most likely the boot drive)
 
Solution
Problems with a drive are unlikely to cause no display at all. He can rule that out by unplugging any HDD/SSD/CD drives as well as any other non-essential devices (the audio header, usb headers, etc).

What are his specs?