Modelling Troubles

I have the main form of the Chest modelled out, however when it comes to bevelling the edges I often have lots of troubles. The most common of which is "warning encountered a non-manifold vertex. Cannot Bevel."From what I understand this happens when you have shapes with more than 4 sides. I went on to fix all polygons making sure they were 3 or 4 sided shapes, This worked for some but not all. I checked all the vertices made sure there were none extra, and made sure all the normals were facing outward as they should be, some weren't so this did help. But still I went on to have the problem.
(also for a day or two every time I pressed 3 to see the smoothed version of the chest, Maya would crash. This was very inconvenient. It stopped after restating my computer, I.T. Crowd advice )