My Pi4B wouldn't boot up the other day and have been trying many different things with no luck. I have everything unplugged from it except the official power supply. With or without the SD card inserted I'm getting 3 long followed by 3 short flashes of the green led and a solid red.
I got a brand new SD card (San Disk Extreme 32Gb) and burned latest Rasbian using PiImager and I am getting the same behavior. I also have tried without the SD card and with the HDMI plugged in. According to the Pi official docs i should at least see a bootloader diagnostic screen - which i don't. So I am thinking maybe my EEPROM or something like that needs to be "rescued"?
I also downloaded the latest eeprom recovery image (https://github.com/raspberrypi/rpi-eeprom/releases) and used the PiImager to create both a USB and a SD version of a recovery. Tried to boot with both and same behavior - as soon as i plug in power it starts the 3long/3short pattern as if its failing immediately. I also burned a SD card from the "Misc utility->bootloader->SD Card Boot" option.
Deep deep in the docs i found the error fo 3L/3S green - "I2C error - Pi 4". Can anyone point me to reasons for this and/or potential resolutions - or did i somehow fry my board...
So I am thinking maybe my EEPROM or something like that needs to be "rescued"?that's what I would do - though if the pattern is the same regardless of the presence or absence of sd card, and it's a pattern that isn't documented - you may have trouble with a rescue flash - still, give it a go