Note: This behavior does not apply to TeamViewer 9 (or later).
TeamViewer waits several minutes after windows-start until it tries to listen on Port 80 (if this Port is not taken by another application). If your application has not taken the Port within that time-frame or the application has not started automatically, TeamViewer might have taken the Port.
You can disable this behavior in TeamViewer version 8. Simply open the TeamViewer options under Extras > Options > Advanced. Enable the option Don't use incoming port 80 (recommended for web servers only) so that TeamViewer won’t try to take the Port again.