MAYDAY MAYDAY.. Help restore my dual channel pls!

Having understood that all (if not most) of you are experts in this
field, I would like to seek your advice pertaining to a persistent
technical problem.

I currently own a P4 2.6, Gigabyte motherboard GA-8IPE1000 Rev 1.0,
with two TWINMOS 256 DDR RAM (PC3200).

Recently I couldn't boot up my CPU, so I suspected my CMOS battery is
dead. True enough, the battery replacement solved the booting issue,
but a new problem arose when my Dual Channel Memory has turned into
Single Channel!. From 512 RAM it became 256 RAM. I did not meddle my
RAM nor the DIMM slots when performing the battery replacement. Its
WAS working perfectly.

I sought the tech staff over at Gigabyte.com but their
"recommended" solutions (e.g. load optimized/ fail safe
settings in BIOS) did not work. I had tried reflashing the BIOS (from
F6 to F11) but to not avail either... I have tested both the the
TWINMOS individually and they are in working perfectly by themselves.
I have also attempted rearranging the dimms... sigh..

HELP!