SQL Server Makes Our Server Reboot!

hi,

we are having this weird problem that can be reproduced easily on 2
out of 2 servers where we've tried:
- we run a SQL Server 2000 stored procedure that processes 2.5 million
rows (big procedure with many cursors)
- when it hits an area of procedure (not always the exact same place,
but in the same area) , the server reboots

I've tried to debug the problem but:
- there are no event log except when it restarts to say 'previous
system shutdown unexpected'
- the blackbox trace I've created is empty
- the perfmon log stops a few seconds before the reboot and shows no
out of whack counter
- we've had the hardware checked by an IT guy and everything looks
fine

The only thing we can see that might have changed is that the disks
and data files were reorganized ..but that's on one machine. On the
other machine were we copied the database to test, we did not do that
and it still rebooted.

I've also run DBCC CHECKDB and everything looks fine. I've scanned all
the hard drive for bad sectors. We've tested the CPUs for overheating.
I've monitored the virtual memory to make sure there was enough.

Any help will be appreciated, we are out of ideas!!

thanks
Guillaume
ps: we are using win2000/SP4 and SQLServer 2000 SP3