>>My notebook computer (an old inspiron 5000e) suddenly has become unstable when I run it with 512 meg of memory. This is actually the max mem this model can handle. Sometimes won't boot. Sometimes boots up OK and then after an unpredictable time will either hard freeze or BSOD on me with a page-fault related "stop". etc. I've got several compatible memory modules of different capacities and have swapped them around. Oddly, the machine seems to run fine with less then 512 meg (i.e., 384, 256) regardless of which manufacturer's SODIMMs I use. But whenever I max out the memory with 2 x 256 SODIMMs, the system becomes unpredictably unstable. When I run the official (boot to DOS) Dell diagnostics with 512 meg, the diagnostics freeze up in progress rather than reporting an error. With less than 512 meg, I can't make it go wrong.
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>>Anybody else have a similar anecdote and a "most likely" cause? Thanks.
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>Try http://www.memtest86.com/ from a bootable CD or floppy.

Indeed... smells like bad memory. And since it seems to work with less memory, the probable culprit is somewhere in the upper half. A faster way to find this out is to swap the cards, if there are two, or even use just the upper one, plugged into the lower location. The machine should freeze much earlier.

The trouble with some ways the bad memory can be bad is that there's very little software can do to catch this sort of error - it freezes first.