Help diagnosing a lockup

[Federico Tello Gentile]

I have used in this machine Fedora core 2 and RHL9 and every once in a
while I experience a lockup. The mouse pointer disappears, the
keyboard lights don't switch, everything looks freezed. I can only
hard reset the machine.
This has happened with RHL9 and with FC2 with the default kernel and
with kernels compiled by myself (kernel.org official kernels unpatched
but I manually remove unneeded options).
It has happened while connected to the net (dial up) and when not
connected. When using some application and when using others.
I have looked in the kernel log and all seems normal (no oops no
panic) until it jumps in the timestamp to the moment I rebooted.
I need help diagnosing the reason for this.
The lockup happened twice one day, but it has been time where in a
week or 2 it has not happened.
I waited a while to see if it comes back, but it does not. I removed
some cron tasks, but it happened again.
Is there any driver that can cause this? I have some "unpopular" hardware.
My video card is old (Diamond Steath 64 DRAM PCI) I think it is using
the VESA driver. I have an internal ISA modem (USRobotics FAXMODEM
Voice  V.90) that I use as a regular serial port (it is not detected
as a PnP card, but I point the system-config-network as /dev/ttyS2 as
a serial port and it dials).
It is a Soyo 7VBA motherboard, with a P3 1 Ghz 256 MB RAM. It has
happened with and without the USB device enabled from the BIOS setup.

It has always happened while I was working at it, that is moving the
mouse, never when I leave it playing music or just turned on but not
sitting at it.
Can it be a mouse driver issue? I have a Genious NetScroll (with
wheel) but I have to use it with the Microsoft intellimouse driver
(serial) so it detects the wheel.
I now believe it is some hardware/driver looping forever but how can I
diagnose this?

Thanks for reading all.