system sees half the ram

I visited a new client today. The puter has an ASUS P2B-F mobo with a P2-350 processor. All the jumper settings are correct for the system bus speed…etc. Problem is at boot up, the bios only picks up half the ram installed. I doubled up on the ram(put in another stick of 128MB) and it is the same, now the sys sees 128MB ram rather than the 256MB installed.
OS is Winnt 4.0 sp4
Any ideas?

Mike