I have an Advent T9304 desk top computer and the sound card does not appear to be functioning at all. The O/S was upgraded from Win XP to Win 7 and this may mean there is a compatibility issue. Is it the case that the Advent CM!9880L sound card is not compatible with Win 7? If so does anybody have an idea where I can purchase in the UK, a compatible sound card for this system? Thanks for your help.

You may well need to re-install the drivers for the sound card as the re-install to Windows 7 would have wiped any drivers and the native ones obviously don't work. Your problem is going to be find drivers as it's a old model sound card and I cound't find anything around for it. Did you get any sort of disk with the PC the might have drivers on it?

Maybe trying contacting the purchase store. Or check on either one of these sites,

Official Advent Support Group
Non-Official Advent Support Forum < I would try posting here first to see if anyone has drivers for you