512MB RAM stick only showing as 256MB?

Why would a 512MB RAM stick only show as 256MB in BIOS?

The RAM in question is Crucial's CT6464Z335. I RMA'd my old stick of the same model when my computer got toasty at the end of April.

The same model previously worked just fine in my PC. The only difference is that I moved from an AMD Athlon XP 2600+ to an AMD Athlon XP 2700+. I've tried different BUS speed and clock multiplier settings to see if that would get the RAM to show as 512MB, but the current setting is the only one which boots the PC past POST.

I've tried the stick by itself, with a 256MB stick, in different DDR RAM slots (there are three on the motherboard), all with no success.

Could a bad video card affect how BIOS reads the RAM? I recently found that my video card went bad and I'm wondering if this could have either damaged the motherboard or somehow interefered with BIOS reading the RAM size.

Arg, I'm so confused. Any ideas?

Well, the 256MB RAM stick works just fine. System boots, motherboard recognizes stick as 256MB. It's only the 512MB stick that doesn't show up at full value.

I called Crucial earlier today (May 31) and received an RMA number for the 512MB stick of RAM. They'll ship me a replacement today or tomorrow. Once I receive it, I'll send my (possibly) defective 512MB stick back and test the new stick. If the motherboard reads the new 512MB stick as 512MB, then I'll buy a new video card. If the motherboard reads the new 512MB stick as 256MB, then I'll buy a new motherboard.

UPDATE: As per post #28 on the "Operation Burnination" thread, Crucial sent a new stick of RAM, which arrived on June 3. The motherboard read the RAM as 512MB, so I ordered a new video card.

Case closed. ^^ Well, at least, the case involving the bad RAM.

Thread locked.