Navigator signal non existant?

My gps has stopped working. I am not very tech savy so i am not sure if i need to update the program of if its stuffed. I was using it as usual. Turned the car off. When i got back in the car & turned nav back on a screen id never seen before appeared. Stupid me didnt read it and just hit the next button. Since then the nav will not show me where to go. keeps saying ''waiting for GPS signal''. I re-installed the software that it came with but still the same result???? Any help would be appreciated!