cubase 5 sound issue

Hi guys,

I am a first time user of this forum. My cubase 5 recently stopped playing sound. I have no idea what I done to it, if anything, and I cannot fathom out the problem. I have selected the correct ASIO to output sound, I have all the correct inputs and outputs selected but still there is no sound. Can anyone please help??
I can hear my midi controller when I open up a new track but I cannot hear any of the sound effects. I cannot hear anything at all in the master section and this has stopped my new album right in its tracks.
As I say, this all started yesterday. Could I have deleted certain codecs to allow this to happen???
Thanks in advance guys,