The fundamental rule for local network connectivity is that computers must be in the same network, meaning they belong in the same Internet Protocol (IP) address range as defined by the network address and its subnet mask. When you change your wireless router's IP address and subnet mask, your wireless Vista laptop loses connectivity with the router.
If you disabled DHCP in your wireless router, and your Vista laptop is configured to obtain IP address automatically, then your Vista laptop cannot connect to your router when you restart it. Your Vista laptop will automatically assign one of unused IP address from 169.254.0.0 to 169.254.255.255 which is the range of automatic private IP addresses established by the Internet Assigned Numbers Authority (IANA).
If you want to connect with your wireless router again, you need to manually assign your Vista laptop with a valid and unused IP address together with your network's subnet mask and the router's IP address as gateway address. You can do this by logging on as Administrator, opening your Vista laptop's control panel, and clicking on Network and Internet.
Click on the Network and Sharing Center and on the left hand portion of the window, click on Manage network connections. Left click Wireless Network Connection, right click it, and click on Properties. Click on Internet Protocol Version 4 and then click the Properties button. Check the Use the following IP address button and enter a valid IP address, your network's subnet mask, and the IP address of your wireless router for Default Gateway. Click on OK, close your Vista control panel and restart your laptop. To continue with configuring your wireless router, open your Internet browser and type the router's IP address on the address bar of your Internet browser.
If your wireless router is setup with Dynamic Host Configuration Protocol (DHCP) enabled and your Vista laptop is configured to obtain IP address automatically, restart your Vista laptop and check if the router has given your laptop the correct IP address. Open a command prompt in your Vista laptop and enter the command ipconfig /all. Look for your laptop's wireless adapter and make sure that its IP address is as what you expect it to be. If not, then there may be something wrong in your router's DHCP settings.
If the IP address obtained by your laptop is within the valid range of your network's IP address range, then you can just type the router's IP address on your Internet browser and open the router's web based configuration program. If not, then you can temporarily assign it with valid network addresses as described in the preceding paragraphs and restart it. Now, you can once again connect with your wireless router and correct its faulty DHCP settings.
To check if your Vista laptop is getting the correct IP address from the router, manually setup your laptop's IP address by following the steps in the preceding paragraphs and checking on the button labeled Obtain an IP address automatically and clicking the OK button. Close your Vista control panel and then restart your laptop. Perform the IP address checking procedure as described earlier using the command prompt to make sure that your laptop is receiving the correct IP address.
The IANA has set aside several blocks of IP addresses that cannot be used in the Internet and designed for use only in private networks. You can choose from any of these private IP address ranges and customize an IP addressing scheme for your network which will accommodate only a small number of computers using a suitable subnet mask. You can look for IP address tables for these IP address blocks in the Internet and select an IP address range that you can use in your home network. You can then use the lower numbers of this range for static assignment by your router's DHCP server and the higher numbers for dynamic assignment to the rest of computers in your network.
If you find it difficult to work in wireless mode, you can directly connect your laptop to your wireless router using the LAN cable supplied when you bought your wireless router. Connect one end of the cable to the RJ-45 slot in your laptop and the other end to any one of the LAN ports of your wireless router. Now all you have to worry about is that the IP address your router is using and the IP address of your Vista laptop are within the same valid IP address range as determined by your network's subnet mask. Once you have determined that your router's settings are in order, you can disconnect the LAN cable and work in wireless mode again.
The important thing to remember is that computers in a network must share the same network address for them to be able to communicate locally. Routers find out the network address by performing a mathematical operation on the binary equivalents of the IP address numbers and their subnet mask. The resulting product is the network address to which the computer belongs to which is the lowest number in the range that appears in the IP address table when using a particular subnet mask. In performing their function, routers are not really interested in particular IP addresses of computers but only concerned with the network address and the IP address of the routers that belong to that network.
Read my other article on a simple IP addressing scheme for setting up DHCP on your wireless home network at: http://publishtoweb.blogspot.com/2011/12/simple-ip-addressing-scheme-for-using.html.
Read an article on how you can recover seamlessly from your laptop's hard disk crash at: http://laptopwriting.blogspot.com/2011/03/how-you-can-recover-seamlessly-from.html.