Cazdebain,
"i've already created different configurations with hidden parts, but connot calculate the mass of each config and the BOM is not displaying things the way i want."
I assume by this you mean you created view configurations, which do not have any influence on the mass properties calc or BOM - these will still be defined from the full assembly.
To calculate mass properties for a group of parts just select the parts you want and then clck the mass properties button. This will show you the mass props for those parts but will not store the results in the file.
bc.