If the 'insert citation' icon in Endnote is greyed out and no longer clickable, this usually means the Cite While You Write tool in Word has been disabled or that Word is linked to Endnote Online rather than Endnote Desktop.

To enable the Endnote tab in Word:

In Word, check that you have the 'Endnote' tab in the ribbon menu on the top of the screen.

If not, please follow 'How do I restore a missing EndNote tab in Word?' FAQ

In Word, the Ribbon tab may be unchecked so you will also need to:

• Click on the File menu and select Options.
• Click on Customize Ribbon and Check EndNote if it is unchecked.

To link Word to Endnote Desktop:

If you have been using Endnote Online it may be that Word is currently still linked to Endnote Online rather than Endnote Desktop. 

To fix this:

• Open Word.
• Go to the EndNote (or EndNote Web) tab, and select Preferences.
• Here, go to the Applications tab.
• Select EndNote.
• Click OK.