There are times when Windows update in Windows 7 / Windows 2008 will not updated the drivers list. This will allow Windows to pull down the newest driver list.

1. Open Task Manager (Right click the tool bar in Windows and click Task Manager)
2. Click Sevices Tab and then Services Button (Bottom Right)
3. Under Name find "wuauserv" The Description field shows "Windows Update"
4. Right click on 'wuauserv' and select Stop. Do not close the Task Manager yet.
5. Open Computer and browse to C:\Windows
6. Right click the folder SoftwareDistribution and select Copy. Paste this to your Desktop as a backup. Delete the Folder "SoftwareDistribution"
7. Go back to Services, Right click "wuauserv" and select Start

Use a  command prompt with administrative rights to use the net command to stop the service and restart it.

net stop wuauserv
net start wuauserv

Now the "Windows Update" button should work