Why is my laptop saying 'Internet Explorer cannot display the web page'? It is connected to a wifi network?

with a allot of people using it, the laptop shows that the signal strength is excellent. When I clicked to diagnose the problem, the response is that 'the DNS server was pinged but there was no response' Any dea how to rectify this so I can use the internet? Someone also suggested that this might be happening because some people are downloading films from websites and you tube.