Can someone tell me if there is a setting that controls app downloading? I can only download if I am hooked to wifi & not when I am on 4G. Thanks in advance.
There is a setting in the Google Play settings menu that says "Update over Wi-Fi Only". Having that option checked may be your problem. But I would think that would only affect the auto-update feature of Google Play. Are you saying that you can't download a new app that you've never installed before unless you are on Wi-Fi?
Is this recent? If so, did you make any changes or add an app around that time?
Do you get a message? If so, can you take a screenshot? If you aren't rooted (or using the leaked ICS) you can use Screen Grabber.