Thank you for posting. Have you tried going into settings -> apps manager -> running apps and scroll down to Play Store and cleared cache & data. Let me know if this helps at all. We'll go from there.
Last week my battery was critically low and because I was not in a position to charge it, I went in to settings and stopped some apps from running. Now, Google Play store will not open, I am unable to update any apps. I have the S3 and am running Android 4.1.2.
Thanks in advance!