server unresponsive after several days

[cleger at scs.carleton.ca]

Greetings list, 

I have a server that serves (pun inevitable) as storage array on my network.
This machine works fine, except for the strange fact that, a few days after
booting up, the machine, while still on, stops responding to pings, to keyboard
input, to ssh requests, and anything else I can throw at it. 

Would anyone like to suggest a troubleshooting approach to this? Has anyone
heard of any such thing happening? The OS is Red Hat Enterprise Linux AS release
4 (Nahant Update 3). Is this, in your experience, more likely to happen due to
the hardware being wonky, or the OS having some bug? 

Thanks in advance, 

Christian Leger