If when opening Skype for Business you are continually asked for your userID and password after every reboot, you can try and remove your saved credentials and re-authenticating.

Method 1:

Ensure Skype for Business is fully closed.  Right Click the Skype for Business icon in the system tray and select Exit or click the cog icon within the application and choosing File - Exit to ensure this.

Click Start

Select Control Panel

Select Credential Manager

Under Generic Credentials select the saved credential that includes

Example: (

Note:  If using Office 2016, it will say MicrosoftOffice16 and you may also see a saved credential that includes  Delete both.

Click the arrow to expand the selection and select Remove

Open Skype for Business

Enter your Office365 UserID (remember to use the format of and password and ensure you select to save the credentials.

Method 2:

Alternatively, try the following:

In Skype for Business, select the cog icon and choos File - Sign Out.

Select Delete my sign-in info

Once deleted, click Sign- In

Enter your Office365 userid and password.  Example:

Click Sign-In

Click Yes to save your sign-in info