Thank you for your reply
I had Qt 5.2 installed but I uninstalled it and installed Qt 5.3 after
Only thing related to Qt is C:\Qt\5.3\msvc2012_opengl\bin so I can use windeployqt.exe more easily, it's recommended in the documentation
(Edit : ) Might be linked : I can't compile anymore, I probably changed something I should not have while trying to fix my dll issue, so now jom.exe returns a "Error code 2"
(Edit 2 : ) It's fixed ! I used the maintenance tool, updated Qt modules and It looks like it has fixed it, I can now compile and deploy correctly !