You probably omitted the Intel chipset drivers.  The chipset drivers define what is on the motherboard and MUST be installed before installing device drivers such as the sound. 

 

For future reference the correct install sequence is (1) Install Windows (2) Install chipset drivers (3) install device drivers (such as the sound). 

 

You can install the chipset drivers now and then the sound drivers.  If that doesn't work you probably need to start over. 

 

If you don't have the chipset drivers  HERE is the Dell download. 

HERE is the download page for the 4550.  Depending on what sound you have will depend on which drivers you install.  If you have the integrated audio (on the motherboard) you need the Analog Devices driver.  If you have an optional sound card you will need the drivers for that card.

It would if the "dummy" would have added the hyperlink.  :smileysad:  Try THIS.