Ok.....can someone please help me!?!?!?

I have a Dell Dimension 4550. I installed Windows 7 about 6 months ago and for whatever reason i lost all of my sound.

There is a red x on my speaker icon.

When i go into device manager under other devices it lists no drivers installed for Multimedia Audio Controller and PCI Input Device.

I have gone to Dells website and tried to install them but nothing seems to work!!!!

Im not sure if it is compatability issue with Windows 7????

PLEASE HELP!!!!!!

Rodney