I had this same problem this go-around. This was the first time I ever had trouble installing Nvidia drivers. I attempted to update through the Geforce Experience software and it took a peculiarly long time. After about 10 minutes, I decided screw this and it messed up everything. I ended up having to boot up, remove all Nvidia software using add/remove programs (if you choose the Nvidia driver through the add/remove, it should take care of everything). Reboot when prompted and then install from the driver from the executable.
If it weren't for firing up shadowplay through it, I wouldn't run Geforce Experience at all.