Try booting to "Safe Mode with Networking" by tapping F8 repeatedly while booting up. That will give you internet access whilst the infection is inactive hopefully.
The best guide to removal of this is here: http://www.bleepingcomputer.com/virus-removal/remove-antivirus-system-pro (Scroll down the page)
Basically you can download and install the free version of Malwarebytes. Update it and run it...all of this while in that mode.
It should get rid of the problem.