not sure why but on my main computer that sound has gone?
checked volumes and things but it has just gone
any ideas?

Have you checked the system volume? Either found somewhere in the control panel or at the bottom right of your screen on on the taskbar. Did you use speakers or did you rely on an internal speaker?

i use speakers
the icon has dissappeared from the task bar

start/control panel/sounds and udio devices

is there something listed at the top of the tab...mine says "C-media wave device" that means my audio device is installed, known and working, if its blank it means its got nothing installed.

in device volume tick the place icon in taskbar option, makes life easier :)

in the sounds tab you can select a windows sound and try playing it when your testing.

double click the speaker icon near the clock now and make sure no sound devices are on mute or turned down.