Peculiar RAM problems with an old Asus mobo setup?!?

I'm have an odd prblem with the memory in one of my PCs. The PC in
questiion is built around an ASUS P3B-F mobo with a P2 450Mhz CPU and
2 sticks of Crucial 256Mb SDRAM PC133....OS is Win98.

Large programs flag up a "not enogh memory" window and starting a game
(like Mobile Rally 1) flags a different window with loads of numbers
and something about low memory.

I ran Norton to see if there was any problems with any hardware and
sure enough the memory fails its test almost immediately. OK, so I
think I've got one dead stick of SDRAM and all I have to do is change
it. Now here's where things start to get odd.

The 2 stick of SDRAM sit in DIMM slots 0 and 1. So I removed the
stick from slot 1 and started the PC. PC saw it had only 256Mb of
RAM. Ran Norton on it, waited and it passed.

Then I pull out the stick in slot 0 and take the stick that was in
slot 1 and put into slot 0. I got exactly the same test result as the
first time on one stick....which means nothing wrong with either
memory stick.

So leaving the stick from slot 1 in slot 0, I put the stick originally
from slot 0 into slot 1. So now they're in the opposite way round to
what they were origanlly. Switched the PC on, say it has 516Mb of RAM
and then run Norton.....the memory fails the test immediately.

OK, this time I move the stick now in slot 1 to slot 2. PC still says
it has 516Mb of RAM, so it knows it's there, but fails the Norton test
again!!!

What on earth is going on??? I don't think it could be a dusty DIMM
slot, the mobo is pretty dust free. The memory works fine if there's
either stick inside, but together they fail and I get all the problems
when using games and large progs as mentioned in the beginning.


Cheers,

Darth Joules