Same here. I returned several days ago after a lengthy hiatus from the game and I haven't been able to use the store at all since then. Sometimes it can take several attempts to even login to the game.
Should I successfully manage this incredible feat, accessing the store is the new challenge. Usually it's a black screen! Every once in awhile, it will load. Too bad everything is 'unavailable' with mystery prices when this happens. I even gave them the benefit of the doubt and attempted all of their ridiculous troubleshooting steps for the issue, all for naught.
But it's totes not their fault. Be sure to contact Microsoft for troubleshooting! And then your computer manufacturer! And if that doesn't work then just build a new computer and try again! If that doesn't work, kill yourself, hope for reincarnation, and then try reinstalling from your new existence!
But it's still not rito's fault.