Do you use multiple monitors? This answer assumes that you do. I have have had the same problem (with QC and other programs as well) when I used my laptop with an external monitor. If I closed out the popup with the secondary monitor in one position, but then repositioned my monitor configuration, the popup tries to open in a monitor that is no longer there.
Say I have my laptop set as my primary monitor and an external monitor on the right. I run QC and the popup is closed out while it was displayed on the external monitor. Then I reposition my monitors so the external one is on the left. The next time i run a test in QC, the popup will try to open in the monitor on the right, even though there is no monitor there.
Ran a test in QC so that popup has opened. Then I opened my Graphics Properties (usually done by right clicking in the empty desktop and selecting Graphics Properties). In the graphics properties, I repositioned my external monitor to the right, left, top, and bottom until I found the popup. Then drag it to the primary monitor and close it from there. The next time it pops up, it will be on the primary monitor.