The problem is most likely in the antenna.
Have you installed a RADAR? The GPS will not acquie a saellite unless it is above or below the bea emitted from the RADAR.
The easiest thing to check is corrosion on the plug where it attaches to GPS.
Look at tour satellite status page. Is WAAS turned on or off? If it is on try turning it off and see if that makes a difference. If the GPS acquires with WAAS turned off, you probably need a software update.
Next follow the antenna wire to the antenna and look for any signs of damage, particularly where any new accessories have been installed. It is also a common point of failure if the cable is stressed near where it enters the antenna.
You may be able to convince your friendly local marine retailer such as West, Cabala, or Boater's World to let you buy an antenna for test purposes and then return it when you are done. You don't have to snake wires all over the boat, simply place the antenna somewhere where it has a clear view of the sky and plug it in.
If the antenna is not the culprit your next step would be to check your software version which appears when you start up the display. If it is not version 2.3.0, get a blank MMC card and download a software update from Lowrance at this link:
SOFTWARE VERSION 2.3.0
It should include intructions on how to install the update.
If that fails, your only option left is to box up the display and antenna and send it out for service.