what kind of sound card are you using?
What ever it is make sure that you are sending the audio to the correct output port[Check your sound card application for this]. Open your control panel and find the flashplayer settings and check the settings and don't forget to delete all the stored data [also try to empty the cash of your browsers, cash is different than history, I am sure you know what to do]. In control panel, also try to find Audio settings in audio and voice tabs, make sure that you are using the correct outputs[In Audio settings try to set all outputs and inputs pointing to your sound-card]. From the same applet [Audio settings] go to Hardware tab and find Audio Codecs, click on it and then click on the Properties button, in the new window go to the properties tab and make sure you have all the necessary audio codecs, and also try to put microsoft related ones in the higher priority. Also check the settings for all codecs to see if something is set to mute or smthng else is wrong. When you are sure you got every thing right click on the OK buttons and close control panel.
Hope I helped
