Well i got this stuck too, but i found a solution …
i installed “Process Hacker” it’s a task manager alternative software …after opening it - right click ShaderCompileWorker.exe and change its priority to High then right click again and select priority> Check “Save for ShaderCompileWorker” (u must do this step fast before ShaderCompileWorker.exe Restarts, it’s automatically restarts every few seconds).
and repeat those steps to UE4Editor.exe and BuildSystem.exe and XGEControlerWorker.exe.
for me after those steps ue4 took about 30 mins to open. Good Luck