I have now hit exactly the same issue and my router is stuck in the following cycle
<<With no ethernet cables connected, just the phone and power:
Green power light
4 Ethernet lights flash amber (approx .5 sec)
Internet light flashes green quickly once
Green power light comes on .... pattern repeats.
With 1 ethernet cable (connected to pc), phone and power:
Green power light
Connected ethernet light flashes green approx 12 times
4 Ethernet lights flash amber (approx .5 sec)
Internet light flashes green quickly once
Green power light comes on .... pattern repeats>>
Seems like a clear hardware / firmware fault, but I can't login to the router to reset / reinstall firmware. Did you find a solution?