PAT - Disabled when using 4 sticks

[AlphaOne]

Here's my setup of the machine:

Dell 400SC, i875p chipset, P4 2.8C ghz (northwood processor) with hyperthreading

RAM - old - 2x512 Corsair value select, unbuffered, non-ECC, memtest86 2.5-3-3-8 (VS1GBKIT400)

RAM - new - 2x512 Corsair value select, unbuffered, non-ECC, memtest86 2.5-3-3-8 (VS1GBKIT400)

 

Here's the problem. My system is running fine with 1GB of RAM, memtest86 at 2.5-3-3-8, dual channel is ok, and PAT is enabled.

I bought a new pair of sticks, the same specs. I replaced the old sticks with a new one, and the memtest results are the same.

BUT, when I put all 4 sticks, the only thing different is that the PAT is now disabled, but still in dual channel.

 

I upgraded the BIOS firmware to A09 (from A06), but the result is the same. BIOS don't allow overclocking (I don't need to).

 

Any help to enable PAT again using all 4 sticks will be appreciated. Thanks.

[RAM GUY]

Unfortunately 875 chipset; per chipset limitation that it will automatically disable PAT when using 4 modules on the motherboard, unless your BIOS setting has the setting to basically manually set it but unfortunately that Dell system doesn't have this option on the BIOS settings.