My
8-core Mac Pro c. early 2008 (now just 3.5 years old!) started acting flaky, crashing whenever I plugged in a cable, revving up its fan to takeoff speed, etc. Disturbing but it mostly worked. Read up online, opened it up and cleaned out (minimal) dust accumulations, reseated the memory cards. It had failed the one time I got it to run the memory diagnostic, pointing to memory FB-DIMMs in Riser A. And indeed, when I booted it up open, the red LED on that riser stayed red, and now I'm running with only the add-on 4 G from OWC.
So (as reported on the web) Apple's supplied Hynix DDR2 memory is failing in large numbers now. Thanks, Apple and others, for letting the DRAM cartel lock out Rambus memory, which had a much better record of compatibility and quality.
Now to order some new memory. My machine is sad without it.