I have just created a new vector layer (line features); used same CRS as all other layers; added new field to attribute table; and saved the new layer as new_garden_cable.shp. I then digitised one feature in the new layer and saved the edits. The attribute table seems OK; the symbol has been set as a simple red line [1.66mm]. The layer is "active" but the layer features are not visible in the map. Adjusting the position of the layer in the Layers Panel has no apparent effect; selecting the layer and using the "Manage Layers Visibility" button to show selected layers , likewise, has no effect. However, when I click on the "Identify Features" button and then click on where I know the digitised feature lies it becomes visible and the Attribute Table opens with appropriate fields and values. Am I omitting some essential step? The only manual that I have is the on-line "QGIS Training Manual Release 2.8" and I have been unable to find an answer therein.
If there is another layer on top of the new one you have created, then you can alter the order of the layers in the 'List by drawing order' table of contents.