IT'S ALIVE! IT'S ALIIIIVVVE!
I've had 3 heavy-duty recording sessions now, about 3 hours each, and only at the end of the last did I get an IRQ BSOD. (I think that may be because I had my USB hard drive on that time.)
This feels miraculous. For the past couple of months, I had gotten a BSOD about every 10-20 minutes, at unexpected times, like
saving. Now I can really push it, adding markers on the fly, undoing and redoing, editing clips--NO PROBLEM!
The main cure, obviously, was finding the right permutation for the memory modules, using MemTest86. It may have been a subtle RAM problem, because it always took MemTest four passes to start finding the errors. Now I pass MemTest over and over again without errors.
I think it helped to move my firewire card into another slot--no longer next to (duh!) the graphics card. Sonar had been very shaky about recognizing my MOTU 896. I often had to go into the ASIO panel and just "OK" it to get the MOTU working. That problem has lessened a great deal after moving the card.
I've been struggling with the Dell computer for over a year, getting blue screens and pops and crackles far too often to record seriously. It's still not the best for audio, but it does work now!
Thanks a million to everyone who has helped in this forum, especially Losguy the Great, but also madcow and others