Why can't I use all the RAM slots available?

Hey folks my PC has the Asus M2N-E SLI motherboard and it has 4 RAM slots total. When I bought the PC, it has 2x 1GB Corsair CM2X1024-6400 memory modules. I just bought another 2GB(2x 1GB) of same brand and same type of Corsair CM2X1024-6400 modules and I experienced failure to boot when I have all four memory modules install; it won't even go past the BIOS screen.

So I tried to install 3GB instead of 4GB and it worked, I was wondering if one of the RAM slots was defective so I also tried to twist memory modules with different slot combinations and it seemed to me all four slots are working properly. So does anybody know why I can't have all four 1GB memory modules installed but 3GB(3x 1GB) works?
8 answers Last reply
More about slots available
  1. could be that one of the sticks of ram is bad? Did you try putting the one that you took out and replacing one of the others with it? I have had that kind of issue before where one of the sticks in the kit was bad and would cause a no boot.
  2. You either got a bad stick, or you ram needs a voltage increase in the Bios.
  3. Welcome to the forums!

    Raise the memory voltage to 2.1v.
    Relax timings.
    Raise the Northbridge voltage.
  4. Thank for the replies guys.

    I am pretty sure that all four modules are working because I've tried every single one of them and tested them with different combinations, they all worked fine with single/double/triple modules installed. Problem raises when I tried to install all four. The symptom is as the following: when I start up my PC, after about 10 seconds I hear a loud beep from my PC, the beep lasts for 2-3 seconds and the minitor stays black; it didn't even get to the BIOS screen.

    I also tried the suggestion above posters have suggested, in my BIOS I changed the DDR2 voltage to 1.95v, which is the highest available in my BIOS and that didn't solve the problem. I'm not pretty sure what evongugg meant by the northbridge voltage and relax timing, is northbridge voltage the CPU voltage or is there another term for it that I'm not aware of? Also what's relax timing? I'm sorry but I'm not too good with computers :pt1cable:

    Anyway, does anybody have other suggestions about what's wrong? Thank you for reading this.
  5. Agree with evongugg. Check the required voltage for your Corsair PC26400. Required voltage to run that those DIMMS is likely 2.0-2.1v. If your MB voltage regulators supply a maximum voltage of 1.95v, that is your likely problem. Your MB is likely a micro with inferior VR's.
  6. Ok guys I finally know what the problem is.

    It is not about bad RAMs or defective slots. I figured this out the harder way... I bought 2x 2GB today and put them into my system and guess what, I heard the same loud beep and my monitor stayed black without showing the BIOS screen. It works fine with 1GB/2GB/3GB installed regardless of how many RAMs I put in and what slots I use, but whenever I try to install 4GB the error above keeps poping up. I read the motherboard and it supports upto 8GB maximum RAM.

    Anyone know what exactly is my problem? Thanks.
  7. Be sure to go into BIOS and set the correct RAM voltage. The MB BIOS will default to 1.8v which is not enough voltage to run four DIMMs of DDR2 in most cases. Most, not all, PC26400 requires 2.0-2.1v to run at advertised speed. If none of this works, you likely have a faulty, damaged MB. RMA the MB.
  8. Allow me to ask you these questions:
    1. Is your motherboard new?
    2. What's your OS?

    Have you already tried these? What are the results?:
    Yellow1: 2GB (installed)
    Black1: 2GB (installed)


    Yellow2: 2GB (installed)
    Black2: 2GB (installed)

    Installing 4x1GB should be fine, since your motherboard supports only one type of memory.

    If your OS is Windows XP 32bit, it will only recognize up to 3GB for some reasons. The excess of 4GB memory installation will not cause any
    usage problem. So if you want to utilize the whole 4GB capacity, you may install a 64bit OS.
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