I got the computer back in 2006, it has a P5N32-E SLI Plus motherboard - the original memory was 2x1GB of the same make and model - CM2X1024-6400, XMS6405v5.1, 800Mhz, but with 5-5-5-12 timing. A few months back (with the original memory from '06) it suddenly started to play up; crashing and blue screening I gave up trying to figure out what was wrong with it and it gathered dust for a while.
I came back to the problem the other week. Determined to get it fixed I managed to catch one of the BSD "IRQ_NOT_LESS_OR_EQUAL" on my camera phone and Google it on my laptop. The advice was it might be a faulty memory module and to shut down and pull individual memory strips and start up and see if that improved the situation. It worked on the first attempt, it started working OK but with 1GB of memory. I then tried different combinations of memory and slots - to check it wasn't a flook, contamination - dust/fluff, a broken socket or miss-seated memory and confirmed it was one faulty module. Not impressed as back in `06 this memory was really expensive!
Nice surprise when I checked out the memory part number on amazon it was still available (if with a slightly different timing of 5-5-5-18). So I ordered a pair to at least replace the existing memory completely should the new strips not get on with the remaining working memory.
When I got it as anticipated my original working 1GB 5-5-5-12 strip doesn't seem to get on with these two new 5-5-5-18 so it was back down to 2GB. But its working fine with the two new memory strips installed. I'm contemplating buying another two to bring it up to 4GB as 32bit Windows 7 Ultimate can cope with that.