Sometimes it take a long time for the GPS to lock in, when you are no where near where it last had a signal or if you factory reset the unit. But it would only take 3-5 minutes with an external GPS.
Sound like a connection problem. Double check the connection fittings that screwed onto the back of the unit. Check all the pins for debris or cobbwebs. Take the connection fitting apart and make sure the cords are all the way in and that the plate goes back on all the way down when the screws are tightened down. Then reconnect to unit and pray to the fishing gods.
If that does not fix it, download the latest firmware patch. Be sure and reset to factory defalt before uploading!!!!!
When you get the cash, I'd add the externial GPS it uses 50 satalites signals and on a good day will gets you within 5 ft. Internal GPS only uses 25 satalite signals and can only get you within 15-25 feet or so.
Join the HB Sideimaging blog (sideimaging@yahoogroups.com) lots and lots of issues addressed on the site. Its the place to go if you do not like reading the manual.

Good Luck.