Ghost drivers
Ghost drivers are either drivers that show up for a device in safe mode in device manager after the device drivers has been removed from the system or there will be a second listing of the device. To better explain what I mean, I am going to give examples.
Example one
In the Device Manager in Normal Mode, it only shows one instance of a monitor driver, but when you boot to Safe mode, it shows two or more monitor drivers. There should only be one listing for the monitor. The duplicates can cause the system to be slow or the video performance will be affected. To fix this, you should delete all monitors in Safe mode, boot to Normal Mode and let the system reinstall it. (depending on the device you delete, you may have to re-install the driver)
Example two
You have deleted the modem in Normal Mode but unable to get the modem to re-install. The modem is not listed in the Device Manager in Normal Mode. When you boot to Safe mode, the modem is listed in the Device Manager. To fix this, remove the device from there as well. When you reboot, you should be able to load the driver, unless you are having other issues.