Well I had the same problem. My Z30 wouldn't connect for a few days. But when I rebooted it, it would connect.
Then again when I used to pull it out & connect again it would be lost.
Again I had to reboot & try.
This happened till I updated OS to the latest, i.e. 10.3.3.2163
So I would suggest you to update it, maybe officially from carrier or by Autoloader.
OK try this once.
Reboot by long pressing power button. Ignore the restart option. Just keep holding the power button & let it turn off.
Now turn it on by again long pressing power button.
Once it's ON, make sure "connect to pc" option is enabled in Settings.
Then plug in the device. Immediately run the Autoloader.
If the process starts, then let it run & complete the update.
If for any reason the update doesn't start, then maybe wait for a few days, 'cause in my case it worked after 2 days.