I just tried another set of CM2X1024-6400C4 ($60 after rebate) to get as much extra memory as I can get, and the PC locks up when even one stick of it is in. Don't even get to adjust any BIOS settings. This is with OC to 2.87Ghz/PC-6400 Dual Channel. BIOS 2302 (BAD for 4GB?).

I tried the new stuff alone in the original orange slots, and the new stuff alone in the unused-until-now black slots, and it works fine.

I see the reports of higher vMCH required by some, and not required by others, so I'm wondering where to go next. This P5W only goes to 1.65V and that's where I had it.

Can hardware revisions in the RAM itself make for incompatibility? I got some DDR for my Compaq that wouldn't work so I swapped it out for similar-to-what-I-had-looking chips from another manufacturer. The parts numbers on these CM2X1024-6400C4 are different from the first set, but the heat spreaders make it hard to see anything.

Would more RAM voltage be required, or just be dangerous?

While I wait for advice, I've gone back to stock BIOS so I can see what happens with 4GB. Unless a miracle happens, I'll have to pop 2 sticks just to change the BIOS again.

Really annoying when just plugging something in doesn't work...