Windows 7: Reinstalling Base System Device driver -- please HELP!

My Dell Inspiron 1521 laptop's built-in microphone doesn't work anymore after I installed Window 7.

I followed suggestions to uninstall the Audio device driver and to reinstall.

I uninstalled the Audio device driver and now my "Base System Device" doesn't have a driver. I troubleshoot and try to let Windows fix the missing driver problem but it failed.

Problems found

Base System Device doesn't have a driver (not fixed)
Base System Device doesn't have a driver (not fixed)
Hardware changes might not have been detected (Detected)

How can I get my Base System Device drivers?

Many Thanks

Have you had a look at Dell's Support site?

Base system device drivers are usualy your card reader. Ricoh or Texas insturments. You can go to Dells site and download card reader drivers or Copy and Paste the hardware id string and we can find a suitable driver I.m sure. I' thinksing your runnning the 32 bit version of seven>? Thanks. Fabe