1.) A quick way to test would be to setup a hotspot using your mobile phone and send in the Wifi credentials via USB.
If this works, that implies the wifi network settings might have some issue we need to look into further.
2.) Make sure the core you use has an antenna attached if you bought the u.fl version
3.) If you have Spark-cli installed, update it to the latest using sudo npm update -g spark-cli and use the command spark flash --usb cc3000 in DFU mode for the patching.
Let me know how it goes 