By default, your Vista laptop is setup to request IP address from a DHCP server in your network. However, this automatic IP address assignment sometimes does not work correctly resulting in lost connection to your network and thereby not having connection to the Internet. Manually setting up your IP address gives your Vista laptop a correct IP address to be able to communicate effectively with the rest of the computers in your network. However, it requires some knowledge of the operation of the Transmission Control Protocol and Internet Protocol (TCP/IP). That your Vista laptop failed to receive an IP address from your router is represented with a yellow triangle with an exclamation point between your computer and your router in your control panel's Network and Sharing diagram.
If you're using a wired or wireless router in your home, then what you have is a local area network and you need to use an addressing scheme that uses the private network address range established under TCP/IP. You define an address range of consecutive IP addresses that starts with the address of your network and ends with the broadcast address of your network. Except the first and the last address in the range, any of the included addresses can be assigned to computers in your network. The valid IP addresses that may be used in your network is determined by your network's subnet mask. Routers perform a mathematical operation on the computer's IP address and its subnet mask to determine as to which network that computer belongs.
To find out what IP address to assign to your Vista laptop, it is of utmost importance that you know the IP address range that your network is using. If you did not use a customized address scheme for your network, then you would most probably be using the default network address range provided by your router. This range typically includes more than 250 consecutive addresses that starts with zero and ends with 255. By using a customized IP address scheme, you can limit the number of computers that can participate in your network by using a unique subnet mask. By doing this, you can have more networks with fewer computers in each network rather than having one big network.
To know what IP address range your network is using, you have to check what the IP address and subnet mask your router is using in your local area network (LAN). If your router is using the default IP address and subnet mask provided by its manufacturer, then probably your subnet mask ends in 0 which means that the range of IP address your network is using consists of 255 consecutive network addresses that starts with 0 and ends with 255 of which the first and the last ones are not normally assigned to any computer.
The IP addresses are constructed with the same first three numbers and varying only with the last number starting from 1 to 254 which are considered the valid IP addresses for your network. You router is typically assigned the first available IP address. So for example if your network's IP address range is 192.168.0.1 through 192.168.0.254 with a subnet mask of 255.255.255.0, then 192.168.0.1 is assigned to your router and the rest are assigned to the other computers in the network. If such is your situation, you can choose one address high above the range, say 192.168.0.251 with a subnet mask of 255.255.255.0 as the IP address that you will set manually for your Vista laptop.
Before you manually setup your Vista laptop's IP address, you need to make sure that your laptop is not being reserved a particular IP address by the router in your network. If your laptop is using a reserved IP address, you need to access your router and remove the MAC address of your laptop from the reservation list of the DHCP server in your router. You can simply disable the line where your laptop's MAC address is given rather than deleting the whole line.
Next, you should free a few addresses high above your IP address range for assigning manually to a few computers. To do this, you have to access your router and modify the address range that your router is set to distribute among the computers in your network. Following on the above example, you should subtract a few numbers from the high end of the range, say you can specify that the address range that your router should assign to computers in your network should be from 192.168.0.2 up to 192.168.0.250. Don't forget to save the changes that you have made to your router's settings.
Logon to your Vista laptop as Administrator, open your Vista control panel, and click on Network and Internet. Click on Network and Sharing Center and on the left panel, click on Manage network connections. Right click the network adapter that you're using to connect to your network, then click on Internet Protocol Version 4. Click on the Properties button then click the small circle that says Use the following IP address. Enter the IP address that you have chosen to use for your Vista laptop and enter the same subnet mask that your router is using. In the Default gateway and the Preferred DNS server, enter the IP address of your router. Click on the OK button then close all open control panel windows.
Your Vista laptop will then reconnect with your network using the new IP address and every time that you turn on your laptop, it won't request for an IP address anymore since it has one already manually set for it. Now when you go to another place where IP addresses are assigned by the router, you have to revert back to your laptop's original setup by repeating the procedure outlined above and by clicking on Obtain an IP address automatically and then clicking the OK button.