Select Inner Join With Where Clause Problems

Hello All,

I have a question about a Select over 2 Tables,
with the Following Scenario (Not all Products (ARTICULOS) haves CARAC's on the CFG_CARAC_ARTICULOS table):

Picture of the tables here:
http://www.pci-baleares.com/pantallazoSql.jpg



We have per example 7 Slots (Motherboard, CPU, VGA Card, RAM, TOWER, etc...)
When we fill the Slot with a CPU-> Then we open the Slot for VGA CARD, we do the Followin Select:

SELECT dbo.ARTICULOS.*
FROM dbo.CFG_CARAC_ARTICULOS INNER JOIN
dbo.ARTICULOS ON dbo.CFG_CARAC_ARTICULOS.ID_ARTICULO = dbo.ARTICULOS.ID_ARTICULO

Ok it brings up ALL Graphic Cards because they dont depends on CPU

Now we go to the Motherboard Slot
And we make the following Select to obtain the compatible Motherboards:
SELECT dbo.ARTICULOS.*

FROM dbo.CFG_CARAC_ARTICULOS INNER JOIN

dbo.ARTICULOS ON dbo.CFG_CARAC_ARTICULOS.ID_ARTICULO = dbo.ARTICULOS.ID_ARTICULO

WHERE

((dbo.CFG_CARAC_ARTICULOS.ID_CARAC = 7) AND (dbo.CFG_CARAC_ARTICULOS.VALOR = 'PCI-E')) AND
((ID_CARAC = 1) AND (VALOR = '775'))

We check the motherboards if they support PCI-E (because we selected a Graphic card of that, and SOCKET 775 because the CPU)

But SQL return 0 Rows, if we do the following Select:
SELECT dbo.ARTICULOS.*


FROM dbo.CFG_CARAC_ARTICULOS INNER JOIN


dbo.ARTICULOS ON dbo.CFG_CARAC_ARTICULOS.ID_ARTICULO = dbo.ARTICULOS.ID_ARTICULO


WHERE


((dbo.CFG_CARAC_ARTICULOS.ID_CARAC = 7) AND (dbo.CFG_CARAC_ARTICULOS.VALOR = 'PCI-E'))

OR

SELECT dbo.ARTICULOS.*


FROM dbo.CFG_CARAC_ARTICULOS INNER JOIN


dbo.ARTICULOS ON dbo.CFG_CARAC_ARTICULOS.ID_ARTICULO = dbo.ARTICULOS.ID_ARTICULO


WHERE

((ID_CARAC = 1) AND (VALOR = '775'))

It return Rows, it happens just if the Where clause haves more as 1 specifications...

Any solution for it? It drives me crazy :D

Thanks and regards
Marc Hägele