Hi and welcome to Computer Hope!
In order for someone to help you diagnose your problem, they are going to need as much detailed information about it.
What operating system are you using?
Do you have an extra NIC Card installed in your motherboard or you just use the built-in one?
Are all drivers properly installed?
Describe the problem exactly. When did it start?
Try also this... In the Command Prompt window, type ipconfig /release then hit enter. After that, type ipconfig /renew then hit enter. Check in your system tray if your Local Area Connection will acquire an IP Address.