my fone has not sub?

my synergy 2150 had no dial tone or ring tone i reset it by turning off at the mains then pressed down the page button as i re plugged it in then after teh 4 bleeps there was a continious bleep,when that ended i then pressed the page button 5 times,apparantly this is how you reset it the hand set is now showing NOT SUB can anyone help,i also have just put new batteries in and fully chargd it