I booted and used my Raspberry for the first time yesterday. I used USB mouse, keyboard and monitor first, enabled ssh and vnc and established connections with my Windows laptop going forward.
I did the same procedure with another Raspberry today. Both have identical SD cards in them which came directly from the seller (got everything together from work). Ultimately I need to run OPC UA server and client applications on them.
Just now I tried booting both at the same time. The one from today works just fine. The one I set up yesterday doesn't do anything. Red light is on, green light blinks 4 times with a few seconds staying on after, then repeating the cycle.
Prior answers to people encountering similar issues suggested the SD was somehow corrupted and start.elf could not be launched.
However, I tried putting the SD card from the other Raspberry in and it shows the same behavior. Also, I can put either SD card in the other Raspberry and it works just fine. Same for the power supply. I haven't found any answer so I would assume this is not a duplicate.
Any help is greatly appreciated.
Update: I managed to boot from a USB stick instead, following the instructions here: How to boot from a USB mass storage device on a Raspberry Pi And it showed the color screen and something after that for a few seconds (rearranging root or something like that, I suppose to start the installation). However, the screen went black, the green light stopped doing anything. Thereafter, whenever I have a USB drive plugged in and connect the raspberry to power, it takes around 30 seconds until the green LED starts showing the usual 4 blinks.