Sony sat nav 92T?

Hi

I turned my sat nav on and it went into a screeen which stated loading, this went on for ages ( i actually thought maybe the item had froze), so i held down the on/off button.
The screen changed to the blue start up screen and from that its never progressed to any of the other screens.

The on/off button doesn't work (only to turn to thr sat nav on), when i press the on/off button to turn the sat nav off, the item stays on (blue - welcome sat nav screen)

The only way to turn the unit off is to use the reset button under the unit.

I've made sure the battery is well charged, I've held the reset button down for 15 secs +, all to know conclusion.

The unit is recognised when i plug it into the computer, but even then it only shows a connecting screen

I'd appreciate it, if anyone can share a practical solution to this matter

cheers in advance

Paolo