system lock up

[chris]

Hi all,

I am somewhat at a loss for how to debug this problem.

Basically my system locks up, its a workstation grade Xeon I do 
development on, essentially, the screen (in X) freezes, the keyboard 
locks, the network locks (it stops responding to ping).  The only 
visible indicator I get when it freezes is sometimes, I see a 4 or 5 
pixel high band of grey/brown that spans the width of the window I am 
currently working in.

I dont see anything out of the ordinary that something is wrong, I can 
let the system sit for days and it runs fine, but when I start doing 
work on it, I start seeing the freezes (it froze up twice in about 3 
hours today).  But sometimes I can work several days in a row without a 
problem.

I would like any ideas on how to debug this.
Thanks in Advance
chris

My System:
Motherboard: IWill DP533
Processors: Dual 2.4GHz Xeon 533MHZ processors
Video: ATI Radeon 6500LE
Hard Drive: several small external SCSI Hard drives
Memory: 1G RAM
O/S: Fedora Core 4

thanks in advance.