2. Using root explorer locate the /efs/imei/ folder. In that folder there should be a file called keystr.
In my case the file was missing which is why the lock screen was missing and was causing my problems.
3. using root explorer create a new file called keystr
(在系統根目錄root 進入 /efs/imei 資料夾 建立 "keystr" 檔案)