Problems with sound device

Hello All,
I couldn't find any information on this problem so I thought I would 
give this list a try.  When I try to play a file (mp3, wav, etc.) I get 
a message box saying "Couldn't open audio" please check that:
1) You have the correct output plugin selected
2) No other programs is blocking the soundcard
3) Your soundcard is configured properly

Every now and then, the file will play fine.  Usually I get the above 
message.  I have a feeling that it thinks the sound card is busy.  How 
can I resolve this prolbem.

Thank you,
Thomas Connolly