Use the Fix-Malf mode or MOSLO boot to fix your filesystem.

To use flasher on the device it needs to be switched off. (to verify that it really is off, press the power button for longer than 8 seconds. When it is really powered off, the led will light up for short period when you quickly press the power button)

When your devide is off, leave it off, start flasher and only then connect it to USB.