you may have moved on from photopad by now... but here goes....
i am also new to photopad and the same thing happened to me. i editted an image and "rendering" went on forever. i terminated photopad in the task manager and restarted. yes, my editting of that image was lost, but as i said, i'm learning. i think i just overloaded my processing of that image with layers and layers of modifications.
as i gained experience i work in a more thoughtful and knowledgeable process, and am really glad i stuck with photopad. it is great - and just what i need.... very powerful. i'm happy to avoid the large learning curves of PS, LR, RT, and others. good luck.
