Why Pentium 4 does not recognize 2GB of ram

Problem I have a Pentium 4 computer with Windows XP, my computer had 512mb ram memory now that I was forced and I put 2GB of ram but I'm not in the computer recognizes the 2GB that I post. What is the reason this problem? Solution Is that the microprocessor is not the problem, your motherboard, you have to see the online specifications as tolerated your motherboard ram.