My server reboots itself.

Hello,

I have a very strange problem an need advice.
My cPanel box reboots itself everyhour. Exactly in 59min it suddenly restarts whole system. Not in 58 min, nor 1 hour. At exactly that time.
I have disabled cron to see if cron is the problem but no luck.
I couldn't see any logs about it in /var/log/messages or anywhere else.
I have run ckrootkit to see if I have been hacked but It hasn't find anything.

What sholud I do???

Thanks a lot.