QUESTION I want to increase the memory in my six-year-old Windows XP PC from 1GB to 2GB to accommodate Windows 7, but keep getting Memtest errors with the pair of 512MB modules I’m using. I receive multiple error reports when I install them, plus stop errors or sudden shutdowns. The machine seems happy to run three RAM modules, but not four.

Crucial advised me to increase the VDIMM from 2.5 to 2.7, which made no difference, and reduce the memory frequency from DDR400 to DDR333 (adjusted to 320MHz), which solves the problem. Why are these problems occurring and how can I run the memory at the correct frequency? Will I need to upgrade my motherboard and processor to install Windows 7? Charlie Horne

HELPROOM ANSWER If your PC has no problem recognising three RAM modules, swap them around to find out whether one of your four slots or Dimms isn’t functioning correctly. (It’s unlikely to be the original ones, since the PC was working previously.)
If no problems are found, it may be that the new RAM modules are incompatible with the existing ones. Each module you use must have the same clock speed. Ensure you have the latest version of your Bios installed, too. Your motherboard can accept up to 4GB (4 x 1GB) of RAM. Consider upgrading your machine using four new 1GB modules rather than two 512MB sticks. This will be more expensive, but it will afford twice the amount of memory and ensure compatibility.

Once you’ve successfully installed the extra RAM, you may want to consider a new motherboard – it’s likely to offer better graphics and sound than you have currently.

See also: How to upgrade RAM - and why

See also: How to fix everything: the ultimate guide to fixing technology

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