On the top right of the screen, click "Change adapter settings".
Right click your wireless network adapter, and click "Properties".
If your network is DHCP Enabled, then look at your IPv4 Address, Subnet Mask and Default Gateway.
If you have another computer on the same network that works properly, run an ipconfig command, and see if the subnet mask and default gateway are the same on both computers.
I will be providing instructions for Windows XP and Windows 7.
If you are using Vista, it is very similar to Windows 7, so follow those instructions.
If your computer connects to other wireless networks, and you have verified that you have the correct frequencies, then more than likely it is not a hardware issue.
Many times when your internet has intermittent issues, but you are still connected to the network, or if you are connected to the network, but not to the internet, you have a DNS server problem.(See step 8)If you determined that you might have an IP addressing issue, this step is for you.Obtaining an address automatically: If you are not receiving your IP address via DHCP, here is how to set your computer to use DHCP: Right click the wireless icon on your system tray, click "Open Network and Sharing Center".What this means is that if you have a 2.4 GHz wireless NIC (which is the most common), it will not work on an A network.If your router is an A router, then you need to get a wireless NIC that supports 2.4 and 5 GHz networks.If you are using Windows 8, you're on your own.(your computer, router, modem, switches, etc).