Asterisk was discunnected suddenly

Hi:
I configured an asterisk server with 2.4G cpu and 1G ram for conference call service but when 5 peoples about 20 minutes were talking together suddenly asterisk was disconnected.May it has happened because low cpu or ram?I saw var/log/asterisk/messages file but everything was going well apparently,asterisk was disconnected suddenly.What 's your idea?Please guide me.