ms-6330 ver2.1

I have a ms-6330 ver 2.1 that came out of a gateway. i bought a new case to put it in. The specs are 386 mb ram 168pin 133 sdram, 950 amd athlon, factory powwer supply, factory sound card, agp nvidia 128mb graphic card, 10/100 network card,56 fax modem. My problem is I just bought a new 512 133 168pin sdram from newegg. I put it in the beside a 128 and 256 which would make 896, but when i turn it on it will load tell it says welcome and reboot its self. What should I do.