system lock-up - RTFM?

[Ian Watts]

My 3.9 workstation has started locking up on me several times a day. 
The box itself has been in use for months.  It may be a coincidence that 
the problem started shortly after upgrading from 3.8.

I've set ddb.panic=1 and ddb.log=1, but each lock-up just freezes the 
system and leaves no clues in dmesg or /var/crash.  It almost always 
happens under somewhat heavy load.  Other than swapping out various bits 
of hardware, which would involve buying new bits, are there any other 
man pages or useful documents that might help me figure out what the 
problem is?  Is this a typical bad RAM scenario?  I don't expect someone 
to solve this problem for me, but any pointers to useful information 
would be appreciated.

Thanks,

-- Ian