according to https://testnet.etherscan.io/, the last block has been mined more than 12 hours ago, whereas before more than one were mined per minute. Has the difficulty changed so much ? Or has the testnet problems ?
The testnet was reset due to various complications, one being a consensus issue between Geth and Parity. You can read about it here:
See the bottom of the page for instructions on running on the new testnet, Ropsten.