Good day MonikaSrivastava1,
1)Is it safe to reset laptop in my case?
Yes, it is safe.
2)Will laptop start working properly after reset?
It should definitely work.
3)Will Defender start to install Security Intelligence Updates and protect me?
It there are updates available that was release by Microsoft then it will install them.
- Will it delete any problematic registry or any other registry which is preventing Defender?
It will repair and replace any corrupted system files.
Have a wonderful day ahead and stay safe.
Sincerely,
Carlo T.