Adding memory causes system non boot

I have an FIC AN11 STEALTH motherboard. I have installed two sticks of pc2100 sdram , one 512mb and one 256mb. They work fine. I would like to increase the sdram by another stick of 256mb.
current installation is
slot 0= 512mb
slot 1= 256mb
slot 2= 0mb
When I install another stick of 256mb into slot 2 the computer refuses to boot up. The board spec indicates that it should be able to handle the additional sdram which would bring the total to 1024mb.
All the memory is good. I have tested them all by interchange. mfg Centon
Is there a bios or board adjustment I have to make to avoid this problem. or something else?

At bootup it stops at "verifying dmi pool"

OS is winme
Athlon Tbird 1500xp
BIOS is Award 6.00 PG firmware 97.114 (12 24 01)
help thanks winndb

Have you tried installing the 2 512mb only?

Thank you for responding.
I already have one 512 and two 256.
Regardless of the slot configuration I put them in, it is as if the board will only accept a maximum of 768. The mobo usage manual says nothing about using the same size in every slot. I also have heard that its generally recommended by many mobo manufaturers, I have searched the web and cannot find any specific such requirement indicated for this board. There are some settings in the bios(voltage, interlace, etc) but tinkering around in there makes me nervous. Any other ideas?
winndb