Hang on a second - just consulting my crystal ball to see what phone you have. Damn - its not working and so I can only give you generic advice.
There will be a button on the base station. Hold it down until, the Base Station beeps. Go into the menu of the handset until you find the Register Handset item and select it.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix corded phones.