Which memory do you use?
I have the same board (with latest BIOS) as you and 2x Kingston KVR667D2N5 2GB (Both Intel and Kingston recommends it).
I have exactly the same problem as you when I use both modules at once, but no problems using only one.
Edit: I should also say that both of my modules have passed memtest86.
I'm using quantity 2 of Crucial Part #: CT25664AA667 • DDR2 PC2-5300 • CL=5 • Unbuffered • NON-ECC • DDR2-667 • 1.8V • 256Meg x 64. This memory isn't officially approved or listed on Intel's site, but is listed as compatible by Crucial.
Intel doesn't list my specific proc Pentium D 805 SL8ZH as compatible, but seems they simply don't include older processors in this list, only new or recent procs. Everything that I've read so far in specification data sheets hasn't indicated any incompatibilities, but has indicated compatible. So I'm at loss here unless someone knows something I don't.
The only thing that's carry over to this board is the memory and processor. I've shed the Geforce Video card, since this board has built in VGA and DVI. I've shed the Linksys PCI nic for the onboard 10/100/1000 on the Intel Mother board.
I'm trying to talk myself out of buying a new processor like the E7400. I don't have anything substantial to indicate the proc is bad. Though it could be, just don't have way to prove it.
Will a motherboard boot at all without a proc or memory installed? I'm not sure what to expect from a known good motherboard in this scenario if one tried to boot. Not sure if anything would be displayed, or if any of the bios sequence would be visible.
I've gone as far as unplugging the SATA DVD and HD, along with the two PATA drives. This leaves no peripherals plugged in. Just the power supply DB9 connected mouse/keyboard.
At this point its hard to do anything without any thing visually being displayed on the monitor.
Will the motherboard/bios error beeps be heard on external speakers plugged into the mini audio port, or would they only be audible an internal PC speaker connected directly to the motherboard?
Why when turning the power on would it run for 3 to 5 seconds, then power down, and restart and run continuously on its own? Mine does this every time and something that's consistent with its current state of build.
Not exactly sure what the next troubleshooting step could or should be.