Always start a new thread for yourself, I moved your post to a new one for you
When you ran the repair tools did you run the reg permissions repair?
Also as a test, make a new user and then log in as that user and try the app store, let me know if that works.
That freaking app store is so easy to break it isnt funny. In Windows 8.0 I couldnt touch any reg key permissions under hkey local machine or the app store freaked out, but hkey current user was fine. But looks like in 8.1 they changed it to not like hkey_current user touched. I may need to make a quick update and block that from 8.1 as well.
Shane