My uncle has an IBM Aptiva S62 Computer - it is a Pentium 2 computer.
There are 3 slots for SDRAM.

I recently installed 3 sticks of 128MB SDRAM for a total of 384MB. The
computer and Windows 98 (as well as the IBM BIOS) do not detect more
than 128MB, however, meaning that only 1 stick is being detected and
used. I have tried re-arranging the RAM sticks and have determined
that each of them independently works in the first slot, but they do
not work together in any combination (that is to say, only 128MB is
detected). If 1 stick of RAM is installed in the second or third slot
only, the computer does not boot.

Does anyone have an idea why all the (384MB) RAM is not working in the
system? If anyone can provide an explanation and steps to resolve this
problem, I will provide a tip.

I know this will sound simplistic, but my professional opinion (over 30
years in the computer industry) is that there is a good chance that the
computer is defective.

There is no reason that what you are trying should not work; each stick
of memory works, the computer can take three sticks of 128 megs of RAM,
and it should be "plug 'n' play" so the only thing left is the system
itself being bad.

To test this theory, you could try three sticks of smaller memory, such
as three 32 meg modules, and if they don't work either, then it pretty
much has to be slots 2 and 3 that are bad.

Looking Forward, denco-ga - Google Answers Researcher