MXQ PRO 4K RK3229 after firmware restore box won't boot

Hello Community

I have a MXQ 4k (not the PRO version) RK 3229 Chip.

I wanted to root the box but it wasn't successful. So I decided to start from scratch and restored the box with Android 6.01 firmware by a USB Cable. The firmware download was successful. At booting up the box said 'failed to mount /mnt/external_sd' it wiped out the data and reformatted it. Then the box stuck at the MBOX logo. I never used a SD card.I even don't have any. I tried different firmware and used the Factory Tool v1.43e and RockChip Batch tool V1.8.

Any ideas what I should do?

Thank you.