Without fully understanding the LED sequence, it sounds like the flash has become corrupted. This can happen if the router is powered off whilst writing to flash (e.g. during config save or factory default reset attempt)
However whatever the cause, Flashwriter can be used to re-load the router with the firmware file in the following zip:
There are some general instructions on using Flashwriter here:
In the event of the flash corruption being so severe that the bootloader is corrupted, whilst using Flashwriter you will need to hold in the reset switch when you power up the DR64, and keep held in until the Flashwriter progress bar is moving.