Thought I'd share this in case any of you run into the same problem.
Borderlands 2 began to crash on me after over 100 hours of gameplay. I would have to verify my game cache and reboot in order to play again or else it would crash as the 2K logo loads up.
Then it stopped altogether and so I seeked some advice at gearbox having done all the regular checks.
The error message I got was this:
Its caused by having a corrupted bin.file although Gearbox are unsure whats causing it, they think the Steam cloud MIGHT be the reason but TBC. So we just need to force steam to recreate the bin.file
As an XP user move the saved games data which is located in folder C: mydocuments/mygames/borderlands 2/willowGame/savedata to a safe location.
Re launch Borderland 2, it will probably crash on the first attempt, it then recreates the needed files so that on the 2nd attempt it will work. There is a slightly different method for Win7 users to get their bin.file back but it is just as simple. Everything is restored (character/game saves/achievements) with the exception of my badass score, but if you want that back immediately there is a method to get that back manually which can be found online.