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...Mimi

I am having the same problem help us. . .
I use my usb to back up some of the important files I have.
and the problem is this base system device driver, only the issue is
because of this usb is not shown on mycomputer. . .
tell as what to do with this base system device driver. . .

Base system drivers are usually card reader drivers- Ricoh or TI or whatever. Download from your models support website.