Apex Tests are running in our production environment just fine and they all pass.  However, in the Test Sandbox nothing is happening. I select tests and all the tests remain at queued without any results for pass or fail. what can i do to get the tests running in the Sandbox. They used to run just as well as they do now in the Production version.

Apex Tests are running in our production environment just fine and they all pass.  However, in the Test Sandbox nothing is happening. I select tests and all the tests remain at queued without any results for pass or fail. what can i do to get the tests running in the Sandbox. They used to run just as well as they do now in the Production version.