Question PC turns on fine but no signal to monitor or peripherals

[Hymn.]

Hi,
A couple months ago I built a pc for a friend of mine and everything was running fine until this morning.
He closed his game and right after his monitor and peripherals just stopped working. The peripherals leds aren't working either but when he turns his pc on they do light up for a split second.

Does anyone know what the problem could be?

PC SPECS:

• Ryzen 5 2600 (cpu)
• TUF B450-PRO GAMING (motherboard)
• ASRock RX 580 8GB Phantom GXR OC (gpu)
• G.Skill Aegis DDR4 16GB (RAM)
• EVGA 500 BR (psu)
• Eclipse P300 (case)

 

[Fix_that_Glitch]

Try unplugging the computer, pull the motherboard battery, let sit for 15 minutes. Replace battery, plug back in and try to restart. What happens?

 

[Hymn.]

Try unplugging the computer, pull the motherboard battery, let sit for 15 minutes. Replace battery, plug back in and try to restart. What happens?

What do you mean by 'pull the motherboard battery'?

 

[Fix_that_Glitch]

On your motherboard there is a nickel sized silver battery on the front. It comes out.

 

[Hymn.]

On your motherboard there is a nickel sized silver battery on the front. It comes out.

Nope, it doesn't work.