[unexpected reboot]

hello,
I have a problem with my server.

Server Specs:

Dual Xeon 3,0 Ghz
4GB DDR2 RAM
400GB HDD
32 IP
cPanel/WHM
Linux CentOS 5.1


I host a site and I have 5-6 uploaders.
When I try to upload some files via FTP (pureFTP), I receive an error for disconnect. Now I check some of my server IPs and they are offline. I try to connect via ssh after some mins. I typed "uptime" and i receive that the server was 4mins UP. I had 23days+ uptime. Something goes wrong.
I see the log files.

logfiles:
...(uploads)
Mar 23 04:02:14 <server-name> syslogd 1.4.1: restart.
Mar 23 06:27:33 <server-name> named[20344]: lame server resolving 'ns7.*.br' (in '*.com
.BR'?): <IP-HERE>#53
Mar 23 06:27:33 <server-name> named[20344]: lame server resolving 'ns8.*.br' (in '*.com
.BR'?): <IP-HERE>#53

Can anyone help me ?

"Lame" DNS servers aren't your worst problem. There's gotta be more in the logs than that. Check your system and daemon logs and login records from some period up to the point where it reboots. And unless your machine is located inside the .br TLD you also might want to look for more signs than just a crash (just in case): look for failed logins or succeeded ones into accounts not regularly used, "weird" loglines in daemon logs, setuid root binaries in temp dirs and do verify your installation (fill in the distro info in your profile please).