Is there a reset button to push with a pen tip type thing? Try that, and if if it doesn't work and you have a suitable spanner disconnect the battery for 10 minutes. Otherwise you will need to try and solve it by delving into software permissions in Android which is a pain.
Have you got a half decent mobile phone? if so go to somewhere with free wifi and download the Google maps for where you are and use that.
Then go home and throw the hateful Navall thing in the bin
