I am not a noob, by any means. I have been doing this for 8 years, reviewing tutorials and Q&A's religiously since I began and I have never encountered this myself, nor has anyone I've seen ever had this issue, I don't even know if it's an issue with Blender. I have a very large and expensive sculpt that I have to finish for a client of his dragon character.
For whatever reason, I can select the whole mesh toggling the "a" key, but can not select it normally using any of the selection tools. It will only select a sparse few vertices outside of the spikes I recently added to his back, but the spikes select normally. It will not even let me select them manually, and I am in vertex selection mode. All of the vertices are visible and none of them have been hidden by any means, they are all part of one object. None of them are overlapping and there are no doubles. I am at a loss for what to do. Where can I upload the .Blend? It's very large.
Just to note two recent events: Blender was running particularly slow and I watched a tutorial which recommended adding Blender to my NVidia control panel, which I did. The second is that I ran into a glitch when I was using the Boolean modifier to add the spikes. Some of them disappeared altogether when I did, but the ones that didn't are selecting normally and the vertices are responding to the selection tools as expected. The mesh I added them to is what's giving me problems.
EDIT: I have uninstalled and reinstalled Blender with no change and this is not effecting other meshes that I have experimented with.
EDIT: I've already tried exporting out the model and hiding parts of it. Like I said, I'm at a complete loss.