Into the TWRP, folow these steps:
1- Go Wipe - Format Data (DON'T BOOT the System Yet)
2- Go Reboot - Recovery
3- Now you flash the System img. Be patient and wait the process. It can take 3-5 minutes, maybe more. (DON'T BOOT the System Yet)
4- Go Reboot - Recovery
5- Now go Wipe - Format Data...