pamela,
I have nothing specific at this point but I do agree that something else seems to be occurring.
One item worth investigating: The Lombard is noted for a higher than normal failure rate for its backside L2 cache. This cache sits on the microprocessor card and will be either 512K or 1MB depending on speed of CPU (333 or 400MHz). This cache can fail outright or be intermittent in its service. It can cause a no-start and/or freeze during use. MacOS 9.2.2 and earlier would have a warning dialogue during a cold startup (not restart) if either the RAM or L2 cache failed during this self-test.
http://docs.info.apple.com/article.html?artnum=51159
MacOS X does not give this startup message. Go to your System Profiler > Hardware Overview and see if it lists your L2 cache.
If you have OS 9.x installed on the HD, cold boot to it and see what happens. Download 'Newer Gauge Pro 1.1' to check the L2 cache (it's 9.x-only):
http://www.macupdate.com/info.php/id/4512
If you don't have a bootable 9.x on the HD but do have a 9.x CD, put Gauge Pro on your HD, then boot to the CD and run Gauge Pro.
Some users with this problem were able to reset the power manager to get a startup, others could not. I am not suggesting this is the problem but with intermittent failure of L2, it could explain some of your problems. It may be coincidence that new HDs are arriving while this failure develops.
By the way, try 'Command-Option-Control-Eject' to force a shutdown.