What model PC? 

However, in general, the install sequence is (1) Install Windows (2) Install chipset drivers (3) Install device drivers (including sound). 

Many, when reinstalling, skip the chipset drivers and these MUST be installed before installing the sound drivers. 

Depending on the quality of your audio card, you may need the high defintion audio driver.  Google for:

KB Article 888111

What I posted applies to your 5150, I have an E510 which is the US version.  ONLY use the Dell SigmaTel drivers.  Do not use IDT High Definition Codec drivers as they will corrupt the Dell SigmaTel.  We went through that a couple of months ago and if the IDT drivers are installed the only way to recover is either a System Restore back to a date prior to installing them or a complete reinstall.  (There was a FAQ on the Desktops Audio section about this, not sure if it's still there). 

SigmaTel was purchased by IDT earlier this year, and I don't know what the problem was but the IDT release "broke" the Dell SigmaTel's.

The 5150 Downloads are HERE