When I try to play a file in Audition 6 the play button turns green but nothing happens.
I have not had a problem with Audition until now. Any ideas?
It's hard to go into detail without knowing more information about your system but it sounds like Audition and your sound card have stopped talking to each other.
Check in the audio control panel for your sound card that the right settings are set to be the default and that the sample rate and bit depth between record and playback match each other.
Then go to Edit/Preferences/Audio Hardware in Audition and make sure that the Device Type is set correctly (ASIO or MME--probably MME if you're using an in-built sound card, likely ASIO with an external card), the the correct devices (i.e. same as the computer audio control) are selected in the drop down menus and, finally, that the bit depth and sample rate match the ones set on the computer audio control.