Random hangs with S2468 Dual AMD (Single OK tho!)

Hi all,

My poor S2468 randomly hangs on me... often under no load... (but often
when i've just clicked on things i think...) But it only hangs when
i've got both AMD Chips installed... Runs fine on one...

Things i have ruled out...

Chips: I can run it on one or the other... both work perfect on their
own...

RAM: I've got two 512MB sticks... i've tried swapping around and
removing one then the other, still hangs..

Too much load on the PSU: I've removed all the pci cards and hdds,
leaving a bare system, it still hangs... So total load on PSU can't be
the problem...

Graphics Card: I've tried running it without my Matrox card, running
it using the onboard ATI video... still hangs...

The system used to run fine for bloody ages!... But then one day, it
started to hang...

Hmmm

Any ideas will be much appreciated.

Cheers
Rich.