S O L V E D !!! After several days looking for information on internet I found the method to recover the boot of the laptop. Following the instructions in the Dell XPS 17 9710 Service Manual on page 76. "Real Time Clock—RTC reset The Real Time Clock (RTC) reset function allows you or the service technician to recover the recently launched model Dell Latitude and Precision systems from No POST/No Boot/No Power situations. You can initiate the RTC reset on the system from a power-off state only if it is connected to AC power. Press and hold the power button for 25 seconds. The system RTC reset occurs after you release the power button". NOTE: If AC power is disconnected from the system during the process or the power button is held longer than 40 seconds, the RTC reset process gets aborted.
Apparently the process went smoothly but after reboot the laptop has no screen (LCD Fault: LED error code 2 amber/7 white). I have followed the following steps: Battery removal and reset: nothing BIOS enter and recovery: not possible due to LCD failure Now I have a nice, advanced and expensive brick. Thanks to Dell.
Dell XPS 9710 LCD screen issue on 1.6 BIOS update