[TYPO3-english] Page tree lost - need your help and advice

[xiaoji zhang]

Hi

I am new here. Our work use typo3 for its website. I am responsible for updating the website. I just looked through the page tree, it suddenly disappeared, When I click on page, it says "the webpage is not found or no accessible". Can you explain what has happened, how to set everything back, please? This is really urgent, I need to add something on the website, I am stuck  here.

Thanks a million,

Xiaoji