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Desktop no display

Hey I have a desktop PC that turns on but absolutely no display.
I have tried everything listed if anyone could give any suggestions that would be much apricated.
Checked following is installed properly: CPU, RAM, Power cables (on motherboard, CDROM, Hard drive), CPU fan.
I know the monitor and HDMI cable works (tested on another machine).
When I plug my keyboard in the peripheral USB (on motherboard with hdmi & vga), the keyboard LED does not shine even when machine powered on with fans spinning?
Could it be that cpu needs motherboards chipset installed onto it?
Could it be the motherboard is faulty like a soldering issue?

Here are systems specs:
motherboard: Asus prime A520m-E

CPU – AMD Ryzen 7 5700G

RAM – 2* ddr4 8gb (no branding)

Power supply – Corsair CV650 ATX

Case – Cit f3 Micro ATX

Drive – 1TB Hard disk (windows installed on)

CDROM

Situation (can read if want):
My cousins PC, was prebuilt gaming PC.
Ordered CPU (AMD Ryzen 7 5700G) of amazon.
Previous motherbaod (asus prime A520m-E r2) was not compatible .
My cousin brough new psu.
My auntie has asked me to fix as cost alot of money spent.
I have managed to get the old pc working.
But now am not abel to get the new components working.
Going to try again tomorrow with fresh eyes
Any help would be appreciated thank you