Hi ​@sotayebi, 

Welcome to Box Community, and glad to help with your collaboration invite! 

Is there an error message when you login to Box.com? If yes, please send us a screenshot in this thread. Meanwhile, if you can successfully login, kindly accept your pending invitation(s). 

  To accept an invitation through the Box web-app: 

1. Login to Box.com and in the left menu of your Box account window, click All Files.
2. In the pending invitations panel under ACTION REQUILRED, hover on the name of a file or folder.
3. To see details about the invitation, click the ellipses, "...", and select View Details.
4. To accept the invitation and gain access to the project's content, click Accept.

Hope it works, and if the issue persist please let us know. 

Thanks for posting!