Hi,
• Have you made any changes to your computer prior to this issue?
Follow the suggestions and see if it helps.
Method 1You may run Network troubleshooter and then check
Using the Network troubleshooter in Windows 7
http://windows.microsoft.com/en-US/windows7/Using-the-Network-troubleshooter-in-Windows-7
Method 2
Step 1 : Safe mode with networking
You may start your computer in safe mode with networking and check if it works fine.
Safe mode with networking
http://windows.microsoft.com/en-US/windows7/Advanced-startup-options-including-safe-mode
Step 2 : Clean boot
If the issue doesn’t persist in Safe mode with networking you may perform clean boot to check if any third party services are causing this issue.
How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7
http://support.microsoft.com/kb/929135
Note : After troubleshooting follow Step 7: Reset the computer to start as usual
Also see:
Use Network troubleshooter event logs to solve network problems
How do I fix network adapter problems?
http://windows.microsoft.com/en-US/windows7/How-do-I-fix-network-adapter-problems