Blizzard warned players back in March that the auction houses for Diablo III on PC would be shutting down today - June 24. The company warned Diablo III players again on June 18 that if they didn't claim items in the virtual game auction by the end of the day today those items or cash would be gone forever.
More details on the final and irrevocable shutdown of the auction house can be found here. To reiterate what Blizzard said back in March concerning the whole ordeal:
"The Auction House is shutting down. You must claim your items from the Completed tab by 6/24. Existing auctions will complete based on the time remaining."
"Items and gold not claimed by this date will be consumed by Treasure Goblins, never to be seen again."
Blizzard disabled the Diablo III auction houses on March 18, locking down all pending auctions and preventing new items from being sold going forward. Blizzard announced its intention to shut down both the real-money and virtual in game auction houses late last year.