Can other device connect to the internet using the same network?
If it can, perhaps it has something to do with your proxy or something? Try this :
Note : Assuming you are using windows vista or higher
1) click start
2) search for "Internet Options"
3) Go to Connection tab
4) click LAN settings
5) Tick "Automatically detect settings". if its already ticked, untick it, click ok, ok again. and redo from step 1 to reenable it.