RPI 4 - Can't get it to work

[Maui_NL]

My raspberry 4b has a problem I can't figure out.

My Pi 4b worked just fine out of the box. Installed Raspian. Used it with RetroPi. Work fine.
And one morning, it just wouldn't turn back on.

Or the green LED turns of immediately and then it 'grows' back on slowly and then stays on constantly.
or both red and green light stay on constantly from the start. But it just never blinks/flashes.

I have tried everything!! Raspian Imager, Noobs, Reboots, EPROOM-fixes, Bootloaders, those HMDI overwrites in the config.txt., Eeprom sticky fixes... Nothing works.

I have also bought new sd-cards of different brands and GB-sizes. And tried different ways of flashing, writing code, formatting cards etc. etc... And the green light just does nothing... it's just on now... not moving...

What else can I do?

[FTrevorGowen]

My raspberry 4b has a problem I can't figure out.

My Pi 4b worked just fine out of the box. Installed Raspian. Used it with RetroPi. Work fine.
And one morning, it just wouldn't turn back on.

Or the green LED turns of immediately and then it 'grows' back on slowly and then stays on constantly.
or both red and green light stay on constantly from the start. But it just never blinks/flashes.

I have tried everything!! Raspian Imager, Noobs, Reboots, EPROOM-fixes, Bootloaders, those HMDI overwrites in the config.txt., Eeprom sticky fixes... Nothing works.

I have also bought new sd-cards of different brands and GB-sizes. And tried different ways of flashing, writing code, formatting cards etc. etc... And the green light just does nothing... it's just on now... not moving...

What else can I do?

What you haven't mentioned is what you're using for a power supply?
Trev.