Can't Upgrade to 2 GB of RAM

I am experiencing problems upgrading my system RAM.

Currently I have two sticks of 512MB of RAM installed on my ASUS A7V600 motherboard.

I want to upgrade to two sticks of 1 GB of RAM for a total of 2 GB of RAM.

Problem is, while the BIOS does recognize the single stick of RAM, Windows XP Pro will not! It either stops booting up at the file KBCOM.DLL or I get an error message saying I need to reinstall Windows! Removing the 1 GB stick of RAM and replacing it with the two sticks of 512 MB of RAM solves the problem!

My motherboard manual says I can use 3 x 184-pin DDR DIMM up to a maximum of 3 GB of unbuffered non-ECC PC2700/2100 DDR SDRAM. There is a note that if I want to use PC3200, I am limited to 2 DIMMS.

The memory I tried from Kingston and PNY was PC2700.
After experiencing problems with two sticks, I decided to try just one stick - that did not work!