Hp Officejet: Pro 8620 Firmware Downgrade 'link'

If your printer is frozen with a blank screen or blinking lights after a failed update:

HP has removed most legacy firmware files from their official support sites. You will need to find community-saved copies. The most commonly sought downgrade versions for the OJ Pro 8620 are: hp officejet pro 8620 firmware downgrade

This prevents the printer from auto-installing new firmware before you finish. If your printer is frozen with a blank