Why is my Raspberry Pi 4 not booting and how to fix it?

Question

I have two Raspberry Pi 4 model B's, 4 GB of RAM (meant to be identical).

I put the SD card in one and the power light is red and the other light is solid green (this is the one that is not working).

The other I put the same SD card into and it boots, screen lights up, keyboard works everything is fine.

The only factor to change is the Pi itself, can I fix this? What is the issue? How do I fix it?

This Pi has worked before, sometimes it boots, sometimes it does not. Have not managed to boot it in a few weeks however it powers up fine.

Note: The screen is black as the night, I get nothing at all. And the PSU cable is the same as the one that works (as in I only own 1 cable, I just change the Pi with all the same stuff, only the board changes in the set up).

Answer 1

When the Pi sometimes boots and sometimes not, there can be numerous reasons for that:

• A broken or unstable power supply. Swap the PSUs of both Pis and light them up to find out. You should also attach a USB multimeter to check the PSU's output voltage.
• A broken PSU cable
• Damaged pins in the SD card bay. You'll need a magnifier to check.
• Problems with the Pi itself: Firmware fault, some electronic element broken, memory corrupt,… Attach your Pi to an HDMI monitor and look for error messages appearing on the screen.

Answer 2

1. Check the power supply. This is the most common problem I've come across.
2. Run memtester to check if you have a memory problem.

If that doesn't help maybe you should upgrade your

sudo rpi-update 

to update your firmware. This is shouldn't be needed under normal circumstances.