Please click on File >Tethered Capture>Start Tethered Capture.
i have restarted it many times but the floating bar will not return
What is the version of Lightroom installed on your computer ?
Also which operating system are you working on, Windows or MAC ?
Please disconnect the Camera once, and close Lightroom.
Open Lightroom , reconnect the Camera and then check.
To hide the window, press Ctrl+T (Windows) or Command+T (Mac OS).
Use the same keys to bring it back up again