I have 2 RAMs plugged in (2GB + 1GB) into DG41RQ mother board. It shows 3GB in bios, but in windows XP it shows only 2GB. I tried reinstalling windows but it does not work. I also tried changing the RAMs in different slots, but still the same problem occurs. Is the problem with the mother board?
Windows XP is notorious for showing incorrect RAM values.
Try running CPU-z (from www.cpuid.com/cpuz.php)
Look under the 4th tab labelled "Memory" - it should show how much RAM is actually installed.
The amount of available RAM shown by XP can also be reduced if you're using integrated/shared graphics.