HP 9000 712/100 problem

group,

not necessarily an HP-UX question,
but maybe some classic hardware experts are hanging around here too:

I have a 9000/712-100 (under 10.20) which used to serve me well,
until a few months ago the box started to "freeze" in full run
every now and then. I.e. the desktop was still displayed,
but everything else (keyboard, mouse, NIC) was dead.
Now the machine even refuses to reboot, with the LED flashing
about twice a second. Manual says 3/4 a second would
mean a dead CPU, but this doesn't quite fit what I see.
I already "reseated" some of the internals
(RAM, mainboard), w/o success.

Any clues what might by the reason,
and, even more interesting, what could be a possible cure ?
I'd hate to dump the machine.

TIA,
MK