Short story: My dad installed Windows 7 family premium edition from Windows 7 family edition. Since, the following happens:

Launching Minecraft in 16w03a crashes and doesn't allow to launch older Minecraft versions.

Strange enough, this never happended to me before.

Precise flow of events:
1-Launching Minecraft in 1.8.9 works fine
2-Launching Minecraft in 16w03a crashes
3-Since the crash, launching any other versions of the game cause crashs
4-Reinstalling Minecraft solves the problem
5-Still, you can take out files from the old .minecraft (tested on saves and resources packs folders) and put it in the reinstalled .minecraft without crashing.

Some crash reports are in the attachment. The 16w03a is the first time launching the snapshot, the 1.8.9 is after launching the snapshot.

There is also a weird .log found in .minecraft. It might be linked with the crash.