Hi there,
The first time you open the editor it will need to compile all of the shaders first. This only happens the first time you run a new editor version.
When loading it will seem like it is frozen at 45% (sometimes 35% and 95% too), but it is not actually frozen. It can take anywhere from 5 to 15+ minutes depending on your CPU speed.
Just open it and then let it sit for a little while, it will load up properly when shaders have completed compiling.