Hi,
1. Have you made any recent changes to the system prior to the issue?
2. What is the exact error message?
3. Is the issue specific to Web Browser?
4. Which is the Web Browser are you using?
5. Are you using wired or wireless connection?
Method 1:
Follow the link mentioned below, perform the steps and check if it helps.
http://windows.microsoft.com/en-US/windows7/Open-networking-troubleshooters
http://windows.microsoft.com/en-US/windows7/Using-the-Network-troubleshooter-in-Windows-7
Method 2:
Follow the link mentioned below, update the network adapters and check if it helps.
Update a driver for hardware that isn't working properly
http://windows.microsoft.com/en-US/windows7/Update-a-driver-for-hardware-that-isnt-working-properly
Method 3:
Follow the link mentioned below, reset the TCP/IP and check if it helps.
How to reset Internet Protocol (TCP/IP)
http://support.microsoft.com/kb/299357
Let us know if it helps.