I'm having problems with my pc xp being slow and jerky. I ran the memtest and, in fact, it found many errors, about 400. At that point I stopped it and ran the memtest individually on two blocks of RAM, removing one at a time.
I ran, for each Ram, 54 passes (more than 10 hours), but it found no errors. Then I redid the memtest with 2 blocks simultaneously and it refound the original errors.
What does it mean if errors are found with two blocks and not with a single set of RAM?
Try booting your system with each stick of ram at a time, the 'bad' one should be easier to spot that way,
And memtest although handy, isnt infallible and is designed for one stick testing at a time.
it maybe that your Mobo is the issue, but try the boot method I suggested first.
It seems you have found each stick of memory performs error-free if used alone, but there are errors when used together. As Moto says, memtest is not infallible, but it more often misses errors than finds non-existant errors.
This points to a BIOS settings or mobo issue. First manually set BIOS memory timings and voltage to match the spec of your mem sticks (and hopefully they are the exact same spec). If that doesn't work, try to relax memory timings or increase voltage (which may not be possible or desirable depending on your specific cpu, socket, memory spec, mobo).
I realized that cpuz shows only a single channel, but having two blocks of RAM, I couldn't understand why it didn't show that I had dual channels. So I changed the position of one block, and I alternated them in the 4 slots, and now the PC recognizes the dual channel and memtest doesn't show any more errors.
I don't know why, maybe having certain blocks in neighboring slots created some errors... Imagine buying a pre-assembled PC with the RAM blocks in the wrong position!
So you did have four slots? Groovy,
for future ref though,
to utilise dual channel, use slots a1+b1, or a2+b2, or all four slots at once
Your Mobo manual will always have the correct configurations info as well
Glad you got sorted man,