I recently acquired a Prime (G8X92AA) which wouldn't go further than the HP Logo screen on startup.
I tried to reflash the firmware using the connectivity kit with the prime in V13 recovery mode. Each time the upload would freeze at 39% and then error out with error number (112) I'm using the official HP USB cable.
I tired different USB ports and as well another pc with exactly the same results. On the final reflash attempt (which again failed at 39%) the screen will now no longer illuminate and the calculator is no longer recognised via USB. To all intents it appears completely dead/inert.
Prior to this I had tried the F,O,C reset trick. The Symb reset trick, the hard reset, all with combinations of USB powered, battery powered, both battery and USB powered.