Unreal engine wont start

my unreal engine wont start i can launch it but when its done loading it there is no window although on the task bar it shows the unreal project browser window is supposed to be open but its not and when i check the task manager it says its not responding. i did once manage to get it to work but when i tried to start a project it just immediately crashed and has been doing the above problum since any assistance would be helpful.