2 raspberry pi 4s not booting anymore

Hi, I have 2 raspberry pi 4's and they are not booting anymore. 1 pi shows a solid green and red light and another only a solid red light. The power to the gpio pins work. I think that it has to due with a charger that I used with it. Is there anything I can do to troubleshoot?

Solid RED = Power is on. Blinking GREEN = Activity. Try another SD card or USB stick as Pi4s can boot from USB mass storage. Connect a display to HDMI0.

I have tried multiple other sd-cards, but no difference. I have ordered a micro hdmi to hdmi cable, which will arrive tomorrow.

USB stick?

To rule out a problem with the SD card connector

Good point, just tried it, but I see no sign something happening

IDU

No video output 😕 , also tried the bootloader img, but no effect.

any suggestions?

Have you tried to reflash the firmware?