CatlinPM

I'm running windows XP, motherboard is and ABIT V17 and I had 512 DDR Ram already installed on the computer. I bought another 512 of DDR Ram both Kingston brand and installed it in my system. When the computer is turned on with both 512 of RAM it becomes very unstable. It will start and load but than when I try to start any programs or the internet I get and error message stating that this program must be closed and am forced to exit from the program. Sometimes I don't get an error message, instead the computer just restarts. I also added a new video card about a week earlier, an ATI Radeon 9250 PCI 256MB DDR which I've also updated the drivers on. Just so you know as well at the same time that I upgraded the video card I had swapped out a 256ddr ram for the 512ddr and the computer had no problems with this. This was the same time that I had updated the BIOS as well. The only time it started to give me problems was when I added the second 512 ddr ram. Sorry to keep rambling like this but I am about ready to pull my hair out... Thank you for any help