Unfortunately, I do not have a manual for the GH-4102. However, most cordless phones get out of range messages at a few points: low handset battery, no power at the base or no dial tone at the base. Other possibilities are the phone base and handset lost the registration or one or the other isn't transmitting/receiving properly.
Things to try: unlpug the base power (from both the wall outlet and the phone) and phone line cord and remove the battery from each handset. Wait a few minutes and then reconnect the batteries and plug in the power and data connections. (Check when you unplug the base power adapter if it was warm; that indicates the unit was at least getting power at that point.) Recharge the handset batteries and then re-register the handsets, if needed.
Consider replacing the handset batteries if they are more than a year old (this includes the time that the phone may have been on a shelf after manufacturing). Try a new phone data cable (RJ11).
Next test your phone line and make sure that you have a dial tone. I like to use an old corded phone with the new phone cord for testing. If there is no dial tone, test the line at another jack. If there is still no dial tone, find your incoming phone line and open the service box. If you have a relatively new service, you will be able to plug your test phone into the service box and test there. If you can't test the line or there is no dial tone at the service box, contact your telephone company. They will test and fix outside problems for free.
If the problem is inside, look at all accessible wiring and make sure that the lines aren't damaged. If only one jack is bad, open the faceplate and fix any loose wires. There are two types of connections. The first holds the conductors under screws and the wire must be stripped back and secured. The other uses a keystone jack. The conductor wires are not stripped but a special tool punches the wires into place. You can find the punch-down tool at many hardware/home improvement stores in the wiring section. See http://www.lanshack.com/wire_phone_jack.aspx
for a picture of the correct wiring for the jack.
If your phone line has a dial tone and the above fixes didn't work, contact the company and get the phone repaired if it is under warranty (usually 1 year). If it is out of warranty, then decide if it is worth repairing or if you should replace the unit.
I hope this helps.