unbricking - Nexus 7 stucks at Google logo

I had Nexus 7 2013 Mobile with Android 4.4.2 running. I tried to update it to recent release 5.0.2 from factory image. When I run command "flash-all.sh", it did not continue at "rebooting to bootloader...". I had to manually stop the process and it still can boot into 4.4.2. After that I tried flashing it manually by running fastboot commands. It then stucked at 'sending system'. I again had to manually stop it. That erase the OS and can boot only into bootloader. I once again tried the luck and run the "flash-all.sh" and it stucked again at the same "rebooting to bootloader..." stage and after manually stopped it, it will not let me boot into anything except Google logo. I can't switch off it, it auto reboot and stop at Google logo. ADB can't detect the device.