outlook 2003 goes offline need help

i have installed outlook 2003 longtime back on our two users laptops running
windows Xp using Exchange 2000 server

its been working fine for the last 3 months , suddenly from yesterday both
of the users face same problem , thier outlook 2003 goes offline even they
are in our LAN
and have connection.
once we press F9 only can be able to send/Recieve ...But still in offline
status

please help me to solve this..

Best regards
Niyaz