Left side of iPod's screen stopped working completely.

Maria Schweinzger, whenever a certain region of the digitizer becomes unresponsive. it is usually caused by a failed digitizer. Of course one always wants to make sure that the flex is properly seated etc. but it is my experience that only a replacement will repair this. In the case of the iPod touch 4th gen, it's a bit tricky and not inexpensive either. This is because the whole front panel needs to be replaced, unless one has an LCD separator machine and other expensive tools at home. Use this guide to fix it. Hope this helps, good luck.