I have moved a wma. file from my yahoo email to Dropbox and it can't be opened To play. What do I do.
Please specify the application you are using.
DropBox doesn't actually play anything itself--it relies on other players in your system. In the case of .wma files, this would have been Windows Media Player but Microsoft have removed .wma support from some of the most recent versions.
Since you're on an Adobe forum, I assume you can get access to Audition. Audition uses it's own codec and should still play .wma files provided you have DLMS Format Support in Edit/Preferences/Media and disk cache.
If for some reason Audition isn't an option, there are various .wma to MP3 converters listed by Google but I don't have personal experience with any of them to recommend any particular one.