could be bad memory,
could not be seated properly or a litle dust in the slot,
(remove and use canned air to blow out slot, reinstall.)
same type of memory? (ecc/non-ecc, edo, sdram, speed)
do you have the manual for the mobo? it will usually tell
you what kind of memory to use and how to fill your slots.
bios memory count correct at bootup?
bios setup showing proper amount of ram installed?
did you follow static precautions while installing memory?
power disconnected while installing?
I like to remove the motherboard to install memory, by
giving it support from behind while installing the memory
chips you lessen the possibility of flexing the
motherboard and causing it to crack.
>Sounds like a bad memory stick to me
>>I recently installed an additional 128 MB memory on top
>>of the 256MB, and when xp boots up it freezes shortly
>>after the string of dots appears. DOS does recognize
>>additional memory. The most recent bios was installed,
>>with no change. Processor is a pentium II, 300 MHZ,
>>an Astoria motherboard. The system works fine with 256