Using Gauge theoretical techniques employed by Lisca for 2-bridge knots and by Greene-Jabuka for 3-stranded pretzel knots, we show that no member of the family of Montesinos knots M(0;[ m1+1,n1+2],[m 2+1,n2+2],q), with certain restrictions on ni, mi, andq, can be (smoothly) slice.To do this, we show that the 2-fold cyclic branched covers of S3 branched over such knots have a very predictable surgery description which can also be viewed as the boundary of a plumbing.The resulting intersection form of that plumbing may or may not embed into the standard negative definite form of equal dimension.We show that the intersection form of the plumbing for each M(0;[ m1+1,n1+2],[m 2+1,n2+2],q) knot will never embed into -I.Then, provided that such a plumbing has a negative definite intersection form, Donaldson's famous Theorem A implies that it cannot embed into a standard negative definite closed, orientable, smooth 4-manifold with the same intersection form. This is enough to obstruct sliceness since, if such a knot is slice, one can construct a smooth rational homology ball by forming the 2-fold cyclic branched cover of the 4-ball branched over the slice disk.The boundary of such a space is the 2-fold cyclic cover of S3 branched along the knot.This can be used to cap off the plumbing thereby creating a closed, orientable, smooth 4-manifold whose intersection form remains negative definite.