Memtest86 must always pass but if for example your bios has slightly wrong settings for ram module it is possible for Memtest86 to pass - and yet you keep getting mystery BSODs. You can google and debug all you like, wont help because real problem lies elsewhere.
So also use Prime95 http://mersenne.org/freesoft/
Unpack zip-file, start it up, options, torture test, pick "Blend" test. Let it run for some hours, like with Memtest86.
I recently had simular problem using 4x1gb pc6400 modules. Chipset can easily handle that, just not with my ram, not at that speed. Had to lower 1 notch - as was recommended by ram maker but why listen, heh. And bye to countless BSOD pointing finger at IE, AV and lots of other innocent programs. Memtest86 always passed.
This is why those who overclock use Prime95 (or should), memtest86 is really very basic. As are the one build into Vista. They dont catch tiny errors, dont push motherboard/ram like P95. Vista sometimes does and then booom.
Look up ram, doublecheck voltage and memory timings - sometimes a bios upgrade is needed for compatibility with specific brands/models. Dont know your bios but any auto-tuning/tweaking of memory should be disabled as well. Some software can do same tweaking in Vista.
Might be a good idea to run sfc /scannow - actually it always returned "corrupted files found" until i used the "correct" settings. After that all is healthy. I almost think files got corrupted during the scan
Edited by Bambo, 08 January 2009 - 08:42 PM.