Can I re-invite a friend who didn't respond to my invitation?

 
Yes. This can be accomplished easily through the My Network functionality.

• Click on My Network, and then Manage.
• Next to the person's name, you'll either see “Pending,” which means an invitation has been sent but not responded to yet, or “Expired,” meaning it's been more than 30 days since the invitation was sent and that it went without a response.
•  Before you can re-invite your friend, you must delete that invitation.