Here is a bit of history..
I unlocked and installed Cyanogen 10.1 awhile back, and TWRP recovery. It's actually dual rom - I can't remember the name of the other ROM.
I haven't used it for a few months and today I charged the battery and used it. It was all good until I checked for update and found that there is Cyanogen 10.2.1. So I clicked download and install.
It downloaded, then rebooted. And when the system is up, I got the pop up saying Google Service is stopped unexpectedly. Some app icons I got on my home screen are still there, but there is no menu bar. There is no home button, no app drawer. So I rebooted, and the same google service error.
So I thought, maybe it's not compatible with 10.2. I rebooted into recovery mode and install 10.1 (the old rom zip file was still on the device) using TWRP. Only took a few seconds and then it says successful/done. To make sure, I also did wipe dalvik cache, then reboot.
Now the system only goes as far as Cyanogen loading screen. That's it. So I hold the power button for a few seconds, then when the device restart, pressed the volumn down button. Then I chose 'reboot recovery'.
It doesn't. It just hangs at Google screen. I tried a few times, the same. So trying to reboot into recovery hangs at google screen, and trying to reboot normally hangs at Cyanogen screen.
As a last attempt, I let the screen hangs on Cyanogen log, connected the device to my Mac, then tried "fastboot devices". Nothing.. empty.
But when I tried "adb devices", I get an entry something like this
List of devices attached 015d2bcxxxxxx unauthorized
./adb shell error: device unauthorized. Please check the confirmation dialog on your device.