Why did our Cisco Firewall reset by itself?

Hi everyone, for the past few weeks our Cisco firewall (ASA5510) has been resetting by itself once a week. can anyone tell me what possible reason that could cause this? Could it be that our firewall needs to be replaced? We're positive that there is no power lost because our switch and other devices are also on the same power strip and those are OK. I've enable logging on the firewall to capture all activities but what level should we set this to? Also, what should we be looking for in the log file? Once last question...I see buffer logging has lots of messages but how do I retrieve it?

Syslog logging: enabled
    Facility: 20
    Timestamp logging: enabled
    Standby logging: disabled
    Deny Conn when Queue Full: disabled
    Console logging: disabled
    Monitor logging: disabled
    Buffer logging: level informational, 42598 messages logged
    Trap logging: level informational, facility 20, 42381 messages logged
        Logging to inside 192.168.1.107
      History logging: disabled
    Device ID: context name "single_vf"
    Mail logging: disabled
    ASDM logging: level informational, 42598 messages logged

Thank so much everyone!