RAM detection problem

Hi,

Last year I bought 3 x Zeppelin 1 GB DDR 400MHz Bulk RAM. My computer started having problems recently and I tested the RAM using Memtest 4.20. The RAM didn't pass the test. Having 3 sticks of RAM (I will name them stick 1, stick 2, stick 3), just one of them proved to be faulty. Even though it's faulty, stick 3 is working fine sometimes, so the problem is intermitent. After removing stick 3 (the faulty one), I have the following problem.

If I plug in stick 1 only, it shows 1 GB (alright).

If I plug in stick 2 only, it shows 1 GB (alright).

If I plug in stick 1 + stick 2 together, it shows 1 GB. (which is wrong! It should be 2 GB)

If I plug in stick 1 + stick 3 (the faulty one), it shows 2 GB. (alright)

If I plug in stick 2 + stick 3 (the faulty one), it shows 2 GB. (alright)

If I plug in stick 1 + stick 2 + stick 3, it shows 3 GB. (alright)

I have 3 slots in my mother board. I tried making all the possible combination, the problem is still there, so I am pretty sure it's not a matter of choosing the wrong slots.

It's not a Windows problem as the issue is present in Memtest 4.20.

My specs:
Motherboard: EP-8K9A7I
RAM: 3 x Zeppelin 1 GB DDR 400MHz Bulk
CPU: AMD Athlon XP 2500+
HDD: Maxtor 80GB