Right, update time.
First and foremost, thanks a ton to all those that helped out, it's greatly appreciated.
Secondly, it wasn't Java, it wasn't the launcher or Minecraft. It was a registry that's been so corroded and corrupted over time that even though I'm the admin on the PC, the launcher wasn't being given admin rights. Not sure of the specific problem, but I did a clean install of Windows and it's working again.
Thanks once again folks, and sorry that I can't contribute more than "clean install" as I have no idea how these things work really.