Dear @Samira_Ghodratnama ,
Sorry to hear that.
Kindly follow the method mentioned in this link Clean_copy. (Thanks @paulinpaloalto)
I followed exact steps mentioned in the post and after several try it worked out.
Steps:
- Rename your current notebook.
- Open clean version of notebook as mentioned in the link.
- Carefully copy everything to the new notebook.
I hope it helps.
All the best.