If D=0 and at least one of D1,D2,D3 is not 0 then according to Cramer's rule the system of linear equations will have
no solutions
By Cramer's rule x=D1D,y=D2D,z=D3D. Given D=0 and at least one of D1,D2,D3 is not 0. Therefore by Cramer's rule we have no possible solutions for this set of equations..