Strange lock-up problem.

Ok, I've built a strange system from parts. It's an Atrend 6310M mobo. It's
an AT, Slot 1 board. I was quite pleased to get it as I have a lot of AT
stuff (cases, PSUs etc) that I've been loathe to throw away. I welcomed the
chance to use some with this board.

I Googled the board and found a manual in .pdf format. It says that the
board supports up to a PII450Mhz and 128MB SDRAM in each of it's two slots.
Great thinks I, I can make a decent machine out of my AT stuff before I
finally biff it (The back room is half-full of AT stuff, including two boxes
of working PSUs).

So I put it together with one 128MB module, 10/100 3Com NIC (I'm on a LAN
here), 8MB AGP card (S3 but it's adequate for it's purpose), ISA
Soundblaster 16, ISA Rockwell 56k modem and a two-port PCI-USB card. There
are pins on the board for a USB header but I don't have the header and there
are pins for a PS/2 header. I *do* have a header for a PS/2 mouse but it
just has four wires in a row and I've tried fitting it either way to the
pins on the mobo and it doesn't seem to work. I don't have a schematic for
the board or a PS/2 port to work out how to/if I can successfully connect
it.

So, the PCI-USB card is there for a mouse (at the moment). I have a couple
of serial mice but they are horrible to use, I want to make this PC
reasonable to use as I have a person in mind for it, I can give them a
monitor with it (14" unfortunately but it's all I have spare and I'm gonna
give it away).

I installed 98SE and it all went perfectly once I'd downloaded a few drivers
I needed. It works great, is snappy and responsive. But.....

I always run SETI CLI on machines I build (as well as Prime95 and, if Prime
fails, Memtest86) as a torture-test. I give a few older machines away or
build machines for friends at no or nearly no profit so I don't want to be
plagued with 'support' calls any more than I can avoid. (I always make it
clear that I will only respond to hardware problems, unless, if they have a
proggy they want installed, they bring it here for me to install)

Ok, the problem. This machine runs Prime95 for 24 hours no problem. It runs
SETI CLI sweet *but*, I have the monitor set to turn off after 10 minutes,
no screen saver. If the machine has completed a SETI WU and it's got the
monitor turned off it locks up. No mouse movement or pounding of keyboard
will wake it. A hard re-set is needed. This has happened three times and
every time the first thing the PC does when it starts is complete the last
10 seconds of a SETI WU and then connect to get another one. It's connecting
through my LAN at the moment.

At any other time I can just move the mouse slightly and the monitor springs
to life, it's only at the conclusion of a SETI WU that this problem occurs
*So far*. Ok, the person I'm gonna give it to isn't going to run SETI but
this could be indicitive of a larger problem. Any Ideas? I was wondering if
it's maybe happening as a consequence of the machine trying to access the
network while the monitor is off? I don't know. The NIC is fine, (3Com) I
pulled it form a machine that it's been functioning in perfectly. In fact,
I'll probably pull the NIC when I part with the machine (although I like to
leave NICs in machines I give away/build for others so I can easilly connect
to me LAN if I need to troubleshoot at any stage).

Any thoughts folks? TIA.
--
~misfit~