You should be able to access the internet in "Safe Mode with Networking" one of the menu choices you get when you tap F8 repeatedly while booting up.
In that mode download, update and run a full scan using the free version of this tool: http://www.malwarebytes.org/mbam.php (It will run OK in Safe Mode).
That should hopefully clean enough of the infection up to enable normal use of your machine.
Run it a second time in regular mode.
Let it remove anything it finds and reboot when asked to.