Had a similar problem with wifi working fine in Safe MOde, but shutting off within 30 secs in regular mode. Tracked the problem back to a recent update from McAfee Mobile Security which added Web Security features. For whatever reason, it flagged by WPA secure Wifi as "Unsecure" and kept shutting it down. By opening Web security in the App and turning off Wifi Security my problem was solved. For the record, it did this at TWO (2) separate (but both COMCAST) wifi locations. I find it hard to believe they were both compromised or being sniffed.