problem adding memory to compaq deskpro en

Hi - I have a problem getting windows 98 to see some additional memory
I have installed in my Compaq Deskpro EN - it had one 128MB stick, I
have just added a 256 MB stick. The Compaq configuration record show
Compaq memory = 384Mb and Windows memory = 128Mb. Windows system info
shows 128Mb. The CMOS setting also show 128Mb and there doesn't seem
to be any way to change it. Compaq memory diagnostics see 384Mb and the
memory tests pass.

I tried swapping the meory sticks around. The system won't boot with
the new 256 Kb stick in the first slot - the bios just beeps at me.

I also tried upgrading the bios from 686P2 v2.11 to 686P2 v3.14 - no
joy.

I suspect the fact that the diagnostics claim to see 384Mb is a
red-herring and there is something incompataible about the memory - it
is a "Standard 'V-Data' 256MB stick of SD RAM, PC133, DIMM, 168 "

I have a 1 GHz Celeron CPU which I think is non-standard - maybe that
has something to do with it?

Any ideas?