Most GPS systems require a first time boot-up where they scan all registered satellites to determine where in the world they are and what satellites to concentrate their navigational efforts on. Try charging the GPS up entirely, and then doing a hard reset of the system (either by navigating to the hard reset in software or by pressing the tiny reset button usually located on GPS units), and then taking the system out under the open sky and letting it run for half an hour or so, making sure it is running in navigation mode (as opposed to setup or media mode). Once it locks properly onto a small subset of satellites, it should not have much difficulty.
If you continue having problems, check to be certain you are running the latest software on the device which can make a big difference. The latest software for the 520 is here: