Use new batteries.
Use the accessory power cord.
Make sure that the unit is in the open and that there is nothing blocking the signal. My unit won't find its location in the cab of the truck. Outside of the vehicle it does find its location. Then it will keep track of the location of the truck when placed on the dash of the truck.
Turn the unit on and if it doesn't lock after 15 minutes, restart and try again.
I had problems initially with my unit locking onto satelites. I don't now. I attributed my problems to operator error...me!
The farther away that the unit is from where it last locked into the location, the longer it will take to scan and lock onto the satelites.
If the unit was last used in Alaska and you are trying to use it in Florida, it will take longer to find its position than if the unit was last used in Miami, Florida and you are trying to use it in Orlando, Florida.
