Linux auto shutdown

[mikewzp]

Hi,
My linux server shutdown by itself once a day.
I don't know why. I have changed the power and checked the memory using Memtest86+.
2.6.9-55.0.2.ELsmp #1 SMP Tue Jun 26 14:30:58 EDT 2007 i686 athlon i386 GNU/Linux
8G mem. 4 harddisks. 350G 500G 350G 500G. Raid 1.
The fans are all working.
What problem do you guys think?
Thanks in advance.

[Infarction]

Does it always happen at the same time? Possibility that someone might have set up a cron job as a prank or something?