ive just put a cd on and its showing as playing and the volume is up but no sound coming out? Help please

Have you made any recent changes in hardware/software?
What is the make and model of your PC? Also make sure your drivers are installed for your sound card.

ive had a new monitor what do i need to do its shows media player as working but as i said no sound.

i dont know what you mean by drivers installed. Its a e machines

What is the model of your e machines? Go to this site and navigate to your model and download your audio driver and install it.
http://www.e4me.com/support/product_support.html

How long ago was the last time you remember the sound working? before or after new monitor? This question might sound dumb, but did your old monitor by chance have speakers built in or attached to them? Also is there a chance that maybe the plug got unplugged from the back of the PC?

NOT SOLVED YET SOEMTHING WAS UNPLUGGED SPEAKERS SO I PUT THE PLUG IN BUT NO GOOD. i DONT KNOW WHAT MY MODEL IS?

Run http://www.crucial.com/systemscanner/index.aspx then send results here

its been sorted with a bit of fiddling around thanks.