X5DP8-G2 problem

Hi .
I purchased on eBay a Supermicro X3DP8-G2 (brand new , but bared and with no
warranty - clever , uh ?) and purchased cpus and ram on another auction .
Info :
2 x Xeon 2800DP/512/533/1.50V SL6VN costarica ;
2 x Intel heatsink and fan ;
2 x Samsung Korea PC2100R-25331-Z M312L6420ETS-CB0 512MB DDR CL2.5 ECC ;
2 x Micron PC2100R-25331-Z MT18VDDT6472G-265C3 US BZAC2LK016 200326 512MB
DDR CL2.5 ECC
(none of them is on Supermicro's page of recommended ram) .

When I power it on , the green led on the mobo lights on , the fan runs and
it gives long , single beeps .
Does not POST .
According to the manual , a memory recognition problem .
I tested it with a single cpu () on cpu socket #1 , each pair at time on ram
bank 1A and 1B .

Since I have no other ECC registered ram , I am not able to see if mobo
works properly .

Now questions are :
have anybody experienced problems with a similar system , particularly with
these memories ?

Thank you in advance

Mauro

I forgot this :
PSU is an Allied Premier model DR-B500E (500W max) with both 20pin to 24pin
and 12V 4pin to 8pin adapters .