i had the exact same problem, i even bought a new controller to no avail. i eventually found the solutionon another forum and now even my old controllers work. after two weeks of searching i can finally breath a sigh of relief.
Right click on Computer
Go to Properties
Click on Device Manager
Right click on the Unidentified Device
Go to Properties
Go to the Drive tab
Click on Update Driver…
Browse my computer for driver software
Let me pick from a list of device drivers on my computer
Windows Common Controller for Window Class
Xbox 360 Wireless Receiver for Windows Version: 2.1.0.1349 [8/13/2009]
Update Driver Warning
Click Yes