Mine happened just 2 days ago, I was wanting to change GFX card, to my new 3850 so i went to delete the Nvidia drivers of my previous 7600GT. I deleted the display drivers but also the Nvidia IDE and ethernet drivers (nForce 570 board) and so upon booting my mouse and keyboard wouldnt work at all. It took me approx. 6 hours to get my system back up with my new GFX card in - all is well now though (R6 Vegas running very nicely) 
