how can I fix my Sat Nav?

my garmen sat nav used to work in ciggarette lighter but then I charged it on my computer now when I plug it in to the ciggarette lighter it doesn't work just comes up with a picture of my computer and the lead what has gone wrong ? It works without plugging in into the lighter but worried it will run out of battery can some one please advise me what I can do .

Ronnie
January 2014