This is for my friend's computer, not mine, so I don't have immediate access to it - although I've been working on it.
My friend has a Dell XPS 630i desktop. She has 6gb or ram - 2 1gb sticks, and 2 2gb sticks. The slots on the motherboard are colour-coded; they alternate black & white.
She has Windows 7. Her BIOS is 1 version behind the current, although I looked at the updates and they do not address this issue.
The problem is this - the ram was working fine, showing 6gb up until recently where it is showing 4gb. The computer is also running sluggishly (hangups and such). It shows as 4gb in bios, as well. I've tested each stick and each slot on the motherboard - they all work, just that the 2gb sticks now show as 1gb. I can't figure out why. I ran memtest from a USB stick, and the memory seems to work fine, it's just less capacity
Is it possible for *part* of a stick of ram to go bad and register as less than its capacity? That's the only thing I can think of.
It would be really odd and extremely unlikely that both would go bad at the same time the same way. Can you try the 2GB DIMM's in another computer? or put other DIMMS in the computer to check? My guess would be that something happened to the memory controller and for some reason is not properly reading the memory or is reading only 1 side of the memory in case the 2GB DIMM's are two sided.