Hola he encontrado un tutorial pero me aparece este error:
14/044/2012 13:44:03 - INFO - Launching Fastboot Toolbox 1.0 by DooMLoRD
14/044/2012 13:44:03 - INFO - Device Status: FASTBOOT mode
14/044/2012 13:44:18 - INFO - Selected kernel (boot.img or kernel.sin): C:\Flashtool\PLAY-GSM-DooMKernel-v14_boot.img
14/044/2012 13:44:18 - INFO - Flashing selected kernel
14/044/2012 13:44:19 - INFO - < waiting for device >
14/044/2012 13:44:19 - INFO - sending 'boot' (8334 KB)...
14/044/2012 13:44:19 - INFO - FAILED (remote: The Device must be rooted first)
14/044/2012 13:44:19 - INFO - finished. total time: 0.000s
14/044/2012 13:44:19 - INFO - FASTBOOT Output:
< waiting for device >
sending 'boot' (8334 KB)...
FAILED (remote: The Device must be rooted first)
finished. total time: 0.000s
Que puedo hacer

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