VS2012 Doesn't start-up anymore correctly after VSAddin usage.

So far I have only a few clues on what happen.

I used VS Addin 1.2.0 for some hours in VS2012. After some hours I had to restart Visual Studio. I think I did it several time before but I'm not sure, maybe not, Imight have only close the solution I was working on and open it again.
So last time I closed Visual Studio, I start it again but the startup stop at the presentation screen.
The presentation screen (showing just the title and version name of Visual Studio) is responsive, but the development interface don't show up even after an hour.
I checked the processes, killed it, start again, did that several times and with and without Administrator mode. No changes.

I uninstalled VSAddin: it worked.

I install VSAddin: it don't work anymore.

I will stop here for now but basically I can't use VSAddin anymore for an unknown reason. I will uninstall it and I'am available for some weeks to do tests and provide data in my specific context. I don't know if it's specific to VSAddin or dependent on a specific context that I have, which is why I report this.