Rockpi4: Flashing green LED and no boot

Hi all,

Got my RockPi4 and tried to boot. I used a 12V 3A source and Ubuntu server on eMMC. It booted fine first time. I tried to attach a 5V 0.1A fan on the 5V pin. Booted fine. Tried an ubuntu update and the system reset in the middle of update. Now when I try to boot the LED is flashing green and nothing happens. What does LED flashing means?