Hello:
I am not sure if the issue has been resolved. I ran into similar problem on HD-H1.0TGL/R5. Unfortunately, Buffalo tech support was very bad and throw the towel saying it is our of warranty and left me on my own to deal with. After strugling for 2 days we made it work. Here is what we did:
Bought another HD-H0.6TGL/R5 on Craiglist and replaced the mother board. The problem did not go away. The DIAG displayed blinking 5 red lights. Then we noticed that the fan was not running on the old unit. We did replace the power supply and the problem solved. My guess, if power supply is defective, then the error display on DIAG is similar to "Flash ROM Error". Please check and see if the fan is working to confirm check the power supply.