l00bsheep 0 Newbie Poster

Sorry but I'm new here and am not very sure if this is the place to ask this. But my problem is that internet works perfectly fine for my laptop but once my sister starts hers, internet frequently shows DNS error and cannot be used. I have tried ipconfig/flushdns and have even gotten an IT guy over to check the network so i know its not a router problem. So could a virus be causing this and how do i solve it if it is. solutions will be greatly appreciated thank you.