There are times when you install an ungrade to a device driver but instead of getting an upgrade you get downgraded in the sense that either you loose on performance or its stoping functioning at all. In situation like this where you are still able to logon with System priviledges, you can roll back the driver.
Here are the steps:

1. Log in with an administrator account
2. Right click on My Computer
3. Select Properties
4. Click on the Hardware tab
5. Click on the Device Manager button
6. Select the device you want to rollback or reconfigure
7. Click on the Driver tab and then click on the Roll Back Drive button