Navigation Scroller Gone!!!

The other day, when composing normally, I somehow accidentally clicked the navigation scroller/ panel thing (I cannot recall the proper name) and dragged it up as if to expand. However, this made the slider disappear and now all I get is a very thin blue line and am unable to select any notes. I have attached a photo as a visual aid.

I really hope there is a way to fix this! I have tried uninstalling and reinstalling the program but nothing is working! I just want things to be back the way they were originally, but even resetting every possible option back to default doesn't work!

Any help would be appreciated!

Many thanks.