You need to manually download the driver for the audio device on your laptop. Windows 7 installation could not automatically configure the driver software for that device (Win 7 most likely did not have the driver in its database).
1. Go to the laptop manufacturer's website (Dell). Search through the driver section. Once you have found the drivers for the specific model you have, download the "audio driver" from the list.
2. If you fail to find software support for that model on Dell's website, you then would need to know what chipset the audio device is, and then download the driver for that appropriate chipset. But, how would you know what chipset your audio card is?
Go to "device manager", look for the audio device that windows can't seem to run. (There should be an exclamation mark next to it). Right click to go to its "Properties". Under the "details" tab, from the drop down list select "Hardware Ids".
The values in the list should contain (in the middle of the text somewhere) something like: "VEN_14F1&DEV_5067"
Here, 14F1 = Vendor ID
5067 = Device ID
(That was my audio vendor and device Ids. You have to find yours).
So, see what the dev and ven IDs are for your audio card. And then go to this website - www.pcidatabase.com
Search for the specific device ID that you have, and click "Search". It will tell you what chipset your card is. It will also have the link to the chipset manufacturer's website for driver. (If it doesn't, google the chipset name for the driver)
It should fix it.
Thanks