I bought a raspberry pi 4 nine months ago, it has worked correctly without problems, but this week it cannot boot anymore.
When the power turns on, the green ACT light flashes four times, and nothing else happens.
I have read the Boot Problems Sticky, checked both the rpi 4 section and the main section, but no joy. Things I have done includes flashing a new Raspbian image and a Ubuntu Server image, trying to use NOOBS, reinstalling the EEPROM, and using another SD card. I have also verified that the 3V3 pin and 5V pin are both supplying good voltage.
The Sticky also suggested the possibility of broken SD connector, but I have no way to test for that. I guess the connector works because using the EEPROM recovery produces a different ACT LED sequence: 2 longs, 4 shorts.
I have read most of the old posts on this site, but none of then seems to be the problem.
Is there anything I can check for? What can I do to fix my pi?