Many users have run into a frustrating issue in which Windows Vista x64 will not boot with more than 4GB of RAM installed in the system. In some cases, startup does not occur at all. In other cases, a blue screen of death (BSOD) or complete system freeze occurs soon after startup. Unfortunately, this issue has no clear-cut fix, but a number of promising solutions have materialized.
Check BIOS settings The first, and generally most successful fix for this issue is to modify your BIOS settings. First, boot into BIOS. This is accomplished by pressing a specific key repeatedly as soon as your computer is turned on (or right after it is restarted). For many computers, the key is F8, but it may be F1, F2, F10, the Delete (del) key or the Escape (ESC) key. Consult your computer or motherboard’s manual or try different keys until you find the right one.
Next, navigate to your CPU settings and select “memory.” Look for a setting called “memory hole” and turn it on, then restart your computer.
If you cannot find that option, or it didn’t work to remedy the issue, boot into BIOS again and look for the “MTRR Mapping” setting. Set this to “Discrete” or “Enablde” and restart.
Remove RAM then perform a Windows Update Microsoft has released software updates that can resolve this issue. Unfortunately, you may not be able to apply these updates if you can’t properly boot your computer. The solution: remove one or more RAM modules until the total is under 4GB (we suggest leaving only 2GB installed), then run Windows Update by clicking the Start button, starting to type Update, then clicking Windows Update. Specifically, you want to make sure that Windows Update 929777 is installed.
Update your device drivers Try booting in safe mode by pressing the F8 key immediately as the computer is starting up. If the system boots and operates properly, a driver problem may be preventing the use of 4GB or more of RAM. Make sure all of your drivers are up to date. The fastest way to do this: click the Start button, start typing Update, then click Windows Update.
Next check the manufacturer websites for any of the installed hardware components you know of: graphics cards, motherboards, or just the manufacturer of your computer. Install any pertinent updates then restart your computer.
Check for bad RAM Check for bad RAM or RAM-related issues using Memtest as described in our previous article.
Worst case: Adjust maximum RAM In the worst-case scenario, you will need to reduce the amount of maximum RAM your system can address to something about 2GB but below 4GB. This can be accomplished launching MSCONFIG (click the Start button and type MSCONFIG then return), then navigating to Advanced Options > Maximum Memory. You might need to remove RAM, as aforementioned, to ensure a proper boot before performing this procedure.