Okay so I've had this issue and i just fixed it..

What i had to do was go to the control panel, go to accounts, then manage credentials, click windows credentials, clear other items (SSO_POP_User) completely, also clear any generic, and windows credentials, cert based credentials.

So when you go to sign in basically it starts from square one. For some reason my path way so to speak was corrupted and put in a loop. When i cleared the above items it allowed me to download apps again.

Which was super weird because yesterday i was able to download skype, and i tried downloading MyTwitch app and it asked me to sign in.. I set it so im always signed in when you enter the initial password to get into the computer. So that was strange.. it also had me set up a new account which was also weird.

But i digress, when i completed the above it fixed the issue and i was able to download apps again.