Internet will not work on my PC.?

[Billy]

I have a custom PC with Microsoft Security Essentials for virus protection. Around 2 weeks ago when I switched on my computer it connected the internet and when I opened my browser (Opera) it told me that the Dns look up failed and that I am not connected the internet. When I open the programme steam my friends list shows up and also shows who is online but everything else on it does not work. I have tried using the internet through other browsers but is does not seem to work. I have tried everything I can from console commands to resetting. Every other device in my house that uses the internet works. The only thing I think could potentially be the problem is when I check security essentials there is lots of blocks for Adware:Win32/BetterSurf. I really need a quick solution because I need my PC to study for my upcoming final exams