Router resets itself

I have a Safecom SAMR-4114 wired ASDL modem router, that has been working
fine. Recently I have been having a problem in that sometimes it can only
keep up a connection for a couple of minutes before the router resets itself
and I lose the connection. I the get the error 'A network cable is
unplugged' appear at the bottom of the screen, it re-establishes the ADSL
connection and then works again for a bit. I am using windows XP with just a
single PC plugged into the router via an ethernet cable. Do I need a new
router, a firmware upgrade, or could it be something else. Any help would be
appreciated. Thanks in advance,

Andy Baker