Thispaperisdevotedtothestudyofsecondordernonlineardifferenceequations.ANonlocalPerturbationofaDirichletBoundaryValueProblemisconsidered.AnexhaustivestudyoftherelatedGreen'sfunctiontothelinearpartisdone.Theexactexpressionofthefunctionisgiven,moreovertherangeofparameterforwhichithasconstantsignisobtained.Usingthis,someexistenceresultsforthenonlinearproblemarededucedfrommonotoneiterativetechniques,theclassicalKrasnoselskifixedpointtheoremorbyapplicationofrecentfixedpointtheoremsthatcombineboththeories.