Computer shut down unexpectedly while unattended.

[Adam Funk <a24061@yahoo.com>]

When I got up this morning I found that my computer had 
mysteriously powered down overnight around 02:50.
Here are are the last log entries before it happened.

/var/log/syslog
Mar 10 02:30:01 garcia /USR/SBIN/CRON[23159]: (root) CMD (test -x /usr/lib/atsar/atsa1 && /usr/lib/atsar/atsa1)
Mar 10 02:40:01 garcia /USR/SBIN/CRON[23166]: (root) CMD (test -x /usr/lib/atsar/atsa1 && /usr/lib/atsar/atsa1)
Mar 10 02:40:01 garcia /USR/SBIN/CRON[23167]: (root) CMD (nice -7 /usr/local/exim/bin/exim -q)
Mar 10 02:50:01 garcia /USR/SBIN/CRON[23173]: (root) CMD (test -x /usr/lib/atsar/atsa1 && /usr/lib/atsar/atsa1)

/var/log/messages
Mar 10 01:50:46 garcia -- MARK --
Mar 10 02:10:46 garcia -- MARK --
Mar 10 02:30:46 garcia -- MARK --

/var/log/auth.log
Mar 10 02:40:01 garcia cron(pam_unix)[23165]: session closed for user root
Mar 10 02:50:01 garcia cron(pam_unix)[23172]: session opened for user root by (uid=0)
Mar 10 02:50:01 garcia cron(pam_unix)[23172]: session closed for user root

Any ideas why, or where else I should look for information
about the cause of this?

Thanks,
Adam