This happened to me before and it used to get fixed on its own. But this time it's been like that for around a month or even more... I actually changed the port to which my PC is connected, but the problem is still there. I cleared my cache a few days ago. But I do not know how to flush the DNS...
EDIT:
How to Flush DNS. Google could be helpful if you actually use it. :)
But even after flushing the DNS, problem is still there...