Have the same issue (Google logo on screen while booting an nothing else. Able to choose factory reset, but it fails with ...make_extf4fs failed on /dev/block/platform/s3c-sdhci.0/by-name/userdata error). Fastboot interface works, but fastboot oem unlock command fails. I think because of not mounted usb storage and impossibility to erase userdata while unlocking. What else should I try to unlock bootloader instead of fastboot oem unlock command?