HP PRIME horribly bricked during update ? (SOLVED!!)

[ytterligare]

UPDATE :

I know my hope is hanging by a thread, but I did some experiment I wanted to write about.

1) Kept the Prime without battery for a couple of hours to discharge a possible residual charge from the capacitors, then insert it again : no change.

2) When plugging the Prime to the power supply there are two cases :

A) With the battery : nothing happen at all, not even plugging or unplugging the prime from the power cord.
B) Without battery : by plugging the power cord, the screen just "flash" for a tenth of a second, like it was trying to start, then return black again.

That's all folks...hopefully someone can pull a rabbit out of a hat...

Andrea

P.S.:
In despair, I ordered a new battery from Amazon, although I measured the original's charge with a Fluke instrument and it was 3.9 V

P.S. 2 :

Tried also :
1) Press ON+Apps+Esc.
2) Press ON+Symb.
3) Press keys ... C+F+O simultaneously and ON key

No change.. :-(