Ext Modem US Robotics

I have an External US Robotics 56K Message Modem which now has the ARQ/ Fax light flashing green. I have never seen it do this before and whenever I try and dial out my PC reports it as not working. Can I unlock this or can you tell me what it is doing. I have tried leaving it of for a few hours wthout much success. Do I chuck it and buy another modem?? Thanks