normally, when poly's disappear...it means there's a problem with your normals, or they're not intersecting all the way.

Make sure the two pieces are intersecting completely and there are no gaps between them. Booleans will not work if they don't intersect.

To check normals, go to Display->Polygon Components->Normals
All normals should be pointing in the same direction for each piece (outwards)
If one or both pieces are not pointing correctly, select the piece, and go to Edit Polygons->Normals->Reverse to reverse them so they're pointing outwards.

Once both pieces have their normals pointing outwards, booleans should work fine.