My thread that I and a couple of guys were working on over the past 2 days suddenly got deleted. Thanks.

My system:
AB9, 2 x 1GB Corsair CM2X1024-6400 @ 800MHz, Vista 32bit

This system runs great, but whenever I try to add another 1GB, all hell breaks loose, with devastating crashes, although BIOS (latest version) recognises the memory ok.

Now I've tested the additional 1GB (of the same kind (says XMS6405v5.1 on it, not sure which version the others, old ones are; I'll find out later today)) on a different computer: no errors.

When I put just that stick in, the inital BIOS memory test hangs, if I skip the test, Vista crashes, as described.

To sum up: all well with my old 2 x 1GB, the extra stick on its own or with the old ones: chaos. Tried other sticks, they're crashing as well.

Any ideas much appreciated.

Have you upped your voltage to 2.0 in the Bios? I've got an AB9 Pro and Corsair XMS2 and Vista 32bit. I had to up my voltage from 1.8 to 2.0 and everything runs smooth as silk!

I haven't tried that out yet, because, infuriatingly, the uGuru options in the BIOS are greyed out, and I seem to remember that I need to clear the CMOS. Which is highly inconvenient, since the jumper is in a very stupid place, it's not only fiddly but I also need to remove my long 8800GTX to get to it.

Anyway, when I put the extra 1GB in again to see if I could raise the voltage, and after I saw that I couldn't then, I just gave it a go, only for the computer to freeze 30 seconds after finishing loading Vista.
I noticed then when I removed the memory again that it had run very hot, not TOO hot, but considerably hotter compared to when it had just finished running the memtest. That struck me as noteworthy and odd.

^Just remove battery to clear CMOS. Also try relaxing the timing and try to keep the RAM speed below 800Mhz.

I will try that. I have noticed that if I leave SPD to decide the timings automatically, it ends up at around 850MHz.
What I don't understand is why it should be ok with 2GB like that, but not with 3GB.