Ok people, I am still dealing with this problem after about a year. I have a biostar ta790gx 128M motherboard and its not letting me put all my ram modules in it. It can hold 4, but will only run right with 3. And the weird thing is, if I put 3 in, 2 in orange and 1 in the very last green slot, it does the same as having 4 in them. I have tried a different power supply, I have taken out the video card, I have replaced this motherboard with a new one from biostar, I have tried a dual core athlon processor, and all is the same thing. I have tested the ram in the old board I replaced and no errors came about. I have tried putting the ram at 2.1 and 2.2 voltage and taking the ram speed at 533. If ANYONE can help me get this figured out, I would greatlyyyy appreciate it.
I have exactly the same issue - will only work with 3 memory sticks but not 4... bizarre behavior... did you find a solution?
Well, right now I have a bigger issue...after replacing the ram, the motherboard and hdd, my computer will not run with the phenom ii anymore. I am guessing this might be the reason why the 4 sticks didn't work, as the phenom ii chip was dying on me. Everytime I try to boot up windows or a livecd of linux, my computer just crashes, even on stock settings....probably not the news you wanted to here, but is my current situation and trying to figure out a fix
Well, here's something that will add to the confusion... I managed to fix my problem :-) .... I originally had exactly the same problem that you reported in that I had 3 1GB memory cards that worked (2 in the green and 1 in the orange slots)... I replaced them with 4 2GB cards and it simply didn't work.... so I tried it with three (2 in the green and 1 in the orange slots) and it did boot up with 6GB available.
I wrote to Biostar and they suggested I test each stick individually, so I booted the system up first with one 2GB stick, then with 2 sticks, then 3, then 4 and lo and behold it's up and running with 8GB available RAM..... The only major difference was that I started memory card placement in the orange slot closest to the CPU and added them sequentially, getting further away from the CPU each added card. I also, after adding the first card, overclocked my memory through the BIOS to 1066.
That's pretty much all I did and now I'm up and running with 8GB - hope this helps you.