These are the most common problems that people run into when using GPS. Also, keep in mind that these and other questions are answered in the GPS manuals that you can take into the field.
1.) The GPS unit can't find enough satellites.
2.) Why won't the GPS receiver connect to satellites?
3.) The screen on the GPS unit or data collector has frozen.
4.) How do I get my GPS files off the GPS unit?
5.) My PDOP is too high and the unit won't allow me to collect GPS data.