I don't have any experience with a Northstar, but look at the antenna and the cable connections. If you have a signal strength screen, take a look at that and see the strength and number of satellites you are getting while you are checking the connections. If only a few are showing and you have a good view of the sky then something is not right in your antenna/cable setup.
By Googling your make and model I noticed that firmware downloads are available. Make sure you have the latest firmware.
That's all I can think of.
Have boat, will travel.