I wanna watch one piece BUT the last time I seen the show was back when It was aired on cartoon network !?

i was the exact same as you, i hadnt watched it since it was on cartoon network either and worst of all i didnt know what episode i finished off at. so what i did (and could work for you aswell) was i started reading the manga, i got up to date with the manga so i had the whole story. now i just pick random episodes and watch them all cos i know i'm not missing any of the story.