1gb pc3200 ddr (high density) not read right in dell dimension 2400

[Ed]

I just recently bought and installed a 1gb pc3200 400mhz ddr non ecc
Standard (high density) memory stick in my dell dimension 2400, however
my coputer only recognizes 512 ram of it. Priot ot the upgrade it just
had the stock 256 stick in the other slot. I left the stock ram in when
I upgraded. Any ideas why it won't read the 1 gig stick right?
thanks
EH

 

[kony]

I just recently bought and installed a 1gb pc3200 400mhz ddr non ecc
Standard (high density) memory stick in my dell dimension 2400, however
my coputer only recognizes 512 ram of it. Priot ot the upgrade it just
had the stock 256 stick in the other slot. I left the stock ram in when
I upgraded. Any ideas why it won't read the 1 gig stick right?
thanks
EH

Because it's high density?

Remove the old module, and try the other memory slot...
that's about all you can do, except clearing CMOS.