I fitted my unit a couple of months ago, grounded the brake cable and everything was working fine until last week. When I now press either the soft Sat Nav button on the screen or the hard Map button, the sat nav starts to load for a second or two then goes back to what it was displaying last.

I have checked the brake cable wire  and that's okay and grounded (It will let me play DVD's).

A bit stuck with what could be wrong, any ideas?