[dba-SQLServer] A real puzzler

[John W. Colby]

My SQL Server spontaneously reboots.  In the past it was once a month, 
then once week or two.  Now it is several times a day.

UNLESS SQL Server is exercised heavily, and then it will not reboot.

That is counter intuitive.

If the issue were a memory issue, SQL Server using all of the memory 
(and it does) would find and trigger such errors.
If it were a heat issue, SQL Server using all of the processors (and it 
does) would cause more heat.

Etc.

If I stop the service(s) it still reboots.

I am at a loss, not only as to cause, but how to troubleshoot.

Any words of wisdom?

Dual chip mother board.
Two AMD processors each with 8 cores (15 cores total)
80 gigs RAM
Windows 2008
SQL Server 2008

-- 
John W. Colby