I've created dozens of skins over the years, but unfortunately, as of late, I've been having problems with getting minecraft to work properly with some of my old skins. (Note: I'm speaking of the Windows 10 version of Minecraft, not the full PC version, which I also own.) For example, I have several skins that I've modified to work with the animated player mod on the full version, that cause the Win 10 version to crash when selected. I know there have been other skins that have given me trouble as well, but this was what just happened to me a few minutes ago. The problem is that I had to reinstall the game once before because I couldn't figure out how to get the game running again. Every time I tried to restart it, it would show the Mojang logo and then die. However, because this happened a second time to me today, I ran through everything a second time, and figured out how to fix it. All you need is your mouse, keyboard and the %AppData% folder.
Step 1: Finding the Minecraft 10 Edition AppData Folder.
First, we have to access Win 10 edition's file system. To do that, we have to get into the hidden AppData folder. To get to the AppData folder, click on your C drive in windows explorer. Then, at the location bar at the top, type in "C:\%AppData%" minus the quotation marks. This will take you to the AppData Roaming folder. We don't want this folder, so at the location bar up top click on the word AppData to go to the main page.
Then, click on the folder that says local, and then in the search bar, search for Minecraft (with a capital M). A folder with MinecraftUWP in it's name should appear. Click on it to enter the app's folder. If more than one appears, you'll have to try the following steps on both folders to make sure the errored file is deleted.
Step 2: Finding the Errored File's Folder
In order to get Win 10's version to work again, we need to delete the file that it doesn't like and set the settings back to a default skin. To do this, navigate to the folder pictured in the location bar in the picture above. It should be labeled minecraftpe.
Step 3: Deleting the File and Resetting the Skintype
There should be an image file in this folder containing your current custom skin. Delete that image and then click on the options txt file to open it.
There will be lots of options inside, but all we care about are two specific settings.
The skintypefull and lastcustomskinnew are the two settings we need to change. set them both back to standard to clear the error from the system.
And that should be it! Open up your Win 10 edition again, it should work and will auto-select Alex as the skin again.