Mine did that after being stored without batteries for some time. It needs to be told approximately where it is by using the map and then let it find the sats.
You may have a faulty aerial but my advice would be to get new batteries leave it in your garden oe somewhere good and leave it for half hour or so and see if that works at all. If you do think it is the aerial then get hold of garmin they should be ok to send one out.
Funnily enough, my SP3 today couldnt get satelites. It ask me if it had been stored without batts just as Blue said. switched off and back on and it was fine.