I too had a similar problem. My Tablo stopped working but the blue LED stayed solid. I pressed the blue reset button but the LED remained solid. I then unplugged the power from the back of the Tablo, waited a couple of minutes and plugged it back in - LED remained solid. Since I was desperate I tried a factory reset - I held the reset button for over 10 seconds - still only a solid LED - never blinked.
I contacted Tablo support then scanned the forum. I saw the notes about the power plugs and checked my supply of power converters. I found one (Kensington K38047US for netbooks - $10 on Amazon) that delivered 12VDC and up to 3A that also had a variety of plugs. I found a matching plug, made sure the voltage was set for 12VDC and plugged it into the Tablo. Voila! The LED began blinking and the Tablo successfully reset! Also, I was surprised to see that I did not lose my recordings (thank goodness).
I checked the voltage on the old power transformer and it showed 12 VDC and over 3A output, so I don’t know why it will not work. But whatever it is is repeatable - Tablo will reset on the replacement supply but not with the original one (I did this a couple of times to confirm)…
So, if you can’t reset your Tablo try finding another 12VDC, 2 to 3A power supply or contact Tablo BEFORE doing a factory reset.