Please don't follow random internet instructions, especially when they're a couple of years old. The instructions you followed were published on August 20th, 2013. They are likely pointing to what is now an out of date driver, and will have been tested on elementary OS 0.2 Luna, since Freya wasn't released until April 2014.
Option 1: (Re-) Install Freya 0.3.1
Freya 0.3.1 was recently released with an upgraded graphics stack. Installing that and sticking to the drivers found in the "Additional Drivers" module is probably both the easiest and safest way. You should be able to access your hard drive and take off any files you want to keep.
Option 2: Purge the driver
- Switch to the TTY using Ctrl + Alt + F1
- Login with your username and password.
- Uninstall the driver.
The article you linked lists the uninstall command as:
sudo ~/Downloads/NVIDIA-Linux-*-325.05.03.run --uninstall