Given the age of this Android-powered GPS navigator and given the Prestigio brand is apparently no more, your best alternative is to start using your smartphone for GPS navigation. The unit is 12 years old, and I'm almost positive unless you were using Sygic or one of the other existing apps on Google's Play Store the maps are no longer being updated. I personally would recommend a Garmin for a standalone GPS navigator since it's what I use, but not everyone has the funds to spare for one of those units.
To restore your Prestigio GV7777 tablet, try reinstalling the Android OS using recovery tools or a compatible firmware flash tool. My Computer Works reviews offers helpful tech support, providing remote assistance for various issues, including device troubleshooting, which might be beneficial for unbricking your tablet. Check their services for personalized, expert help.