Epox 4BDA problems (pc2100&pc2700)

Hi everybody,
First of all forgive my poor english ,I'm French ;o)

Since 2002 i use this 4BDA motherboard with no problems at all,except in
this new case :

it's made for PC1600 SDRAM or PC2100 DDR memory modules ONLY,and for 4 years
i've used a PC2700 512 MB memory module without ANY problems.
Last week I decided to upgrade my RAM up to 1Gb and so bought 2 memory
modules PC2100 512 MB...and NOTHING WORKS.
When starting my computer ===>black screen and all LEDs on with no beeps at
all (using one or 2 PC2100 or one with PC2700).
going back to single PC2700 ====> everything is getting OK.

Why is it happening? Strange fact is that when i use RAM modules made for
this motherboard it doesn't work and when i use one not made for it ....
it's ok.

I ve tried other PC2100 modules with the same result .

Thanx for ur help ;o)