This is usually caused by the protective charging circuit.
If a battery is dead and you connect the TT to a charger the battery can drain too much and a "fuse" blows.
There is only one way of checking:
Since you have two similar devices at hand it will be easier.
Dismantle both and make sure the working one is fully charged first.
Take the full battery and connect to the "bricked" TT - you might have to use a hair dryer to heat the battery a bit which makes it easier to remove in case you don't want to mess too much.
Get the parts together so you can switch that TT back on.
If it turns on you know it has a blown charging circuit, if it still stays dead you got a brick.
In case it does work you have two options to "fix":
a) the really lucky ones can see the blown parts if they burnt on the circuit board - you can then compare to the working circuit board and seek replacement parts, but it will be hard to get them.
b) check Ebay for a device with a broken screen, since most of them are exchangeable you can evan aim for a better model like the Go730
Last option for hard core solutions is to remove the batery and to bridge from the battery connector to the charging lines of the device, but it is not recommended as there is no protection anymore and a faulty charger will completely destroy the device.