Hello and welcome to the forums
For doing a clean install follow this steps:
1_Download and install DriverSweeper from here :http://www.guru3d.com/category/driversweeper/
2_Uninstall your current Nvidia driver from add/remove apps and restart and boot to safe mode
3_In safe mode open Driver sweeper,click on Nvidia and then click clean and restart and boot normally to windows
4_Download and install the latest ATI drivers from www.amd.com and after the installation,restart and done.