Try this:
Firstly, boot your computer to the Safe Mode menu screen.
To do this with Windows 8, this link should prove useful. Once there, enable Safe Mode with Networking. If you run another version of Windows, ignore the link and keep reading:
http://www.bleepingcomputer.com/tutorials/start-windows-8-in-safe-mode/
You do this by repeatedly pressing F8 as soon as you boot up. Once there, use the arrow keys to highlight Safe Mode with Networking. Continue to boot from there, by pressing Enter. You will now see some drivers being loaded. There will be a pause at some point. This usually lasts for no more than 30 seconds.
Start Internet Explorer, and when the program is open, click on the Tools menu and select Internet Options.
Now click on the Connections tab.
Now click on the Lan settings button.
Where it says Use a proxy server for your Lan, ensure there is no tick in the box, then press the OK button to close this screen. Now press the OK button to close the Internet Options screen.
If that's all okay, remain in Safe Mode and try this...
These download links may prove useful:
Junkware Removal Tool:
http://www.bleepingcomputer.com/download/junkware-removal-tool/
AdwCleaner:
http://www.bleepingcomputer.com/download/adwcleaner/
This video shows the products being used:
http://www.youtube.com/watch?v=dvnGAjWNSuk
Once you’ve run them, download the free version of Malwarebytes' Anti-Malware, to try and ensure that nothing has been left behind. Install it and get updates, then run a full scan:
http://www.filehippo.com/download_malwarebytes_anti_malware/
Hope this helps.