|How do you connect to internet? Wired or wireless or USB Mobile?|
Has it ever worked or is this a new connection?
Is the connection shared via a router or are you direct connected to a modem?
Have you checked in devicemanager for any problems with your NIC?
Give us a clue because what you have provided so far isn't enough to even begin diagnosing your problem. It could be anything from faulty hardware to incorrect configuration, to virus infection or operating system corruption.
Goin' Fishin' (Some day)