If its the issue when loading with the launcher if you go into task manager and scroll down you can see two applications running as Minecraft and Minecraft Launcher (I believe but it'll say Minecraft) just end those two tasks and it'll fix start loading right away. Though it is annoying to do so.
Its weird for me it says it uploads my skins perfectly, but when I got into a single player world, it doesn't show my skin it shows Alex, and when I mess around with the skin settings it turns me into Steve.
If its the issue when loading with the launcher if you go into task manager and scroll down you can see two applications running as Minecraft and Minecraft Launcher (I believe but it'll say Minecraft) just end those two tasks and it'll fix start loading right away. Though it is annoying to do so.