My nexus 5 froze during use so I forced shutdown. When I turned it back on it stuck and the google logo. I tried to factory reset from fastboot but when i select recovery the screen just goes blank (i don't see the android robot with the exclamation) and I have to manually shut it down. I also tried to unlock the bootloader to flash the factory image but when I select "Yes" to unlock the bootloader the same thing happens (the screen goes blank). Can anyone help with this?