S.M.
Been there done that!! I went to Target and got a plasma or lcd screen cleaning kit. You use the duster and then you SPRAY THE CLOTH with the spray and give it a little elbow grease and it will come off. I used the tip of my nail covered by the cloth and it came right off. The handle end of a fork would work too. The kit was $10 and has lasted for a really long time!! I hope this works for you!! Good Luck!!