Question Pc on, keyboard and mouse on but no signal

[Darkfade]

Hello, I’ve recently built my brother a system and I have been having problems with it not boosting

Specs:
R7 3700x
Asrock Steel legends b450m
750w evga GQ
Rtx 3080
16gb 3600 geil
2tb Samsung 970 evo

The pc turns on; everything is on including the mouse and the keyboard leds but no display, the vga light is on and the 3080 fans ramp up and down. When I plugged in my 4070 the pc works fine.

 

[Lutfij]

750w evga GQ
Rtx 3080
You're advised to run a near 1KW unit when running a system with an RTX3080 in it, due to transient load spikes. Looking at the parts list, it looks to me that you put it together using used parts, how old is the PSU?

the vga light is on and the 3080 fans ramp up and down. When I plugged in my 4070 the pc works fine.
The power draw for both cards aren't the same.

 

[Darkfade]

750w evga GQ
Rtx 3080
You're advised to run a near 1KW unit when running a system with an RTX3080 in it, due to transient load spikes. Looking at the parts list, it looks to me that you put it together using used parts, how old is the PSU?

the vga light is on and the 3080 fans ramp up and down. When I plugged in my 4070 the pc works fine.
The power draw for both cards aren't the same.

the power supply was new and bought through new egg