No sound from web browser to soundcard

I have recently come across a problem, just lately websites like youtube with streaming video or audio are muted whilst the video playback is fine, I refer to this being only on my Soundcard, I have a Trust 5.1 surround sound card, A USB Wave Driver which I use for headphones, The soundmax audio driver which runs my intel chipset onboard audio, & ATI HD Audio drivers via HDMII output on my 4670 Graphics card. All of the rest of these play the audio from youtube fine, And All (including Trust 5.1 soundcard) Play perfectly with all my normal players (WMP11, Winamp, VLC, Nero Showtime, Core media player, & video splitters Movie making software), To add this is the case with all my browsers (IE 8, Firefox 3.0.11, Wyzo, Cometbird) it’s really odd, I have seen similar posts on various forums and none seem to share the same problem I am having, I have checked all my settings twice and as my soundcard works with normal media and the other sound devices on my system play wem media fine I am just confused as to why it affects only my main speaker system, I was unaware the problem existed till yesterday as I normally use headphones for web based media, so I am not sure how long it has been this way, I only installed this system this week as my previous hdd died and I purchased a WD 1TB Caviar Green, and because I had all my programs backed up I put it together pretty much the same as my other HDD.

I have Dell Dimension 5000
Intel pentium 4 HT Dual core 2X 3.0ghz Processor
4gb ddr3 Ram (4 X 1GB Modules)
ASUS ATI EAH 4670 HDMI/VGA/DVI 512mb Graphics Card
WD Caviar Green 1TB
Windows XP SP3

I have tried a few fixes which have worked for others who have similar problems, but not the same, but the registry values they were missing and advised to repair are all present in my system, I have tried uninstall/reinstall of flash player ( and all adobe products), Java and even my soundcard but to no avail, I have made sure all my updates are current and installed and have run anti malware software/ Malicious software programs to see if they can pick anything up but no evidence of foulplay, Please if you can help I could use some advice.
I hope I have not left anything out but feel free to ask for any further information.
Thanks in advance. RGK.