Suddenly silent

The sound was workibng fine on my machine until today...I've checked the connections, checked the properties in control panel, checked the volume levels on the system and in windows media player - and I don;t know what else to check. Any suggestions?

Just thought - the only thing I can think of that I've done since I last used th ecomputer with sound was installing Avast virus protector. Could a virus protection program mess with sound?

Restart the computer. I've had that happen from time to time. A restart always seems to bring it back. No reason why, as far as I know.

Tried that, doesn't fix it. I think it might be something to do with windows media player; I've been testing it with a music CD, and a couple of times it's said that it's experiencing an error and has to close.

I've had the same warning pop up again: "Windows Media Player cannot play the file. The Player might not support the file type or might not support the codec that was used to compress the file."

Does that mean anything to anyone? It was working fine yesterday...

Lost sound on my Dell E1705 with non factory installed Windows Vista Ultimate 32bit. Everything worked fine for a long time until I installed 4 GB of memory. I went to Dell's site and dounloaded updated Vista drivers for the soundcard and flashed the motherboard. Don't know if that was the reason for the problem, but it fixed it. BTW, be sure you check for the correct sound provider or mother board install in your system. I didn't and even bought an upgrade from Creative thinking that was what was on my system. It wasn't and finally realized mine was the other choice. Dounloaded that one and everything worked fine.

Everything should be up to date; the computer was built only a couple of weeks ago, and everything was checked to make sure it was cpmpatible.

...and it's started working again. I disabled the sound card and then enabled it again - seems to have done the trick. Cheers for the suggestions