IDM not downloading — diagnose it in three steps
No video panel, no capture, or a server error are different problems with different fixes.
Clicking and getting no IDM window has three distinct causes, and each one has its own fix.
No video panel above players
The advanced integration is unchecked or the extension is disabled. Enable Use advanced browser integration under Options → General, then restart the browser. Also check Options → File types: the streaming formats must be listed there, otherwise IDM intentionally ignores them.
Direct links open the browser downloader
Check that your browser is ticked on the General tab and that the file type you are downloading appears under Options → File types. You can also hold Alt while clicking to force IDM, or Insert to prevent it from catching one specific link.
Servers refuse, "403 forbidden" or zero speed
This is a server-side rule, not an IDM problem. Some hosts block segmented connections or require a session cookie from the browser. Work around it by using IDM's built-in manual Add URL with the referrer filled in, or lower the connection count to 1 or 2 for that specific download. For streaming sites with expiring links, refresh the page and grab the video again instead of resuming a stale URL.
Scheduler and grabber as alternatives
For streams IDM cannot capture, the Site Grabber downloads whole galleries or all files of one type from a site, and the scheduler runs queued jobs when your connection is idle. Both work without the video panel.