Newly installed RAM, some not recognized

I've seen posts related to memory problems on my specific system before but this problem is beyond what I have seen posted . . .

Model: emachines T5212
Chip: Intel Pentium D CPU 2.66 GHz
2.67 GHz
896 MB of RAM (that's what it shows with both sticks installed)


My system ships with 2 sticks of 512 mb ddr2 (533), in upgrading I purchased two identical modules of 1 GB ddr2-533 (pc2-4200) memory. My system will auto detect the first new module but will never detect the second. If I put the old memory back in the open slot it will detect it--and only it (the 512 stick).

The bios doesn't recognize the second module as installed at all. Thanks in advance for your help!!