Go to Tools -> Internet Options -> Connections -> Lan Settings
Under Proxy Server
If 'Use Proxy server' is checked and you are not using a proxy server (you most likely are not unless on a corporate network) this will stop the browser from connecting to the internet. If it says 127.0.0.1 for address it was changed by a virus.
To look for add-ons that may be causing issues, go to tools -> manage add-ons
Look through the list of ad-ons and see if anything looks "out of place / doesn't belong" they should all be listed with the development company's name.
Go to Tools -> internet options -> advanced
Under 'Browsing' -> uncheck enable third-party broswer extensions