I am having the same issue. This appears to be the symptoms described by others back in November.
Have tried - bnet repair, running as admin, deleting various cache and vars files and repairing again, restart of computer and all networking, graphics driver rollback and reupdate
What works - Starting a custom game, adding ai, letting it go for a few seconds, then leaving. This makes my collection available, the store to appear etc etc.
Something on the Blizzard side is misconfigured or broken, again, in the same way it was 4 or 5 months ago.