It sometimes becomes necessary to manually renew your IP address. If you suddenly realize you do not have an Internet connection, you can often simply right-click the computer icon in the task bar near the clock of your XP desktop (If this icon is present). This will go through a process of resetting your IP address.
But if you do not have this option, you can go to START>RUN and type cmd. At the command line type ipconfig /release (or winipcfg /release in earlier versions of Windows). Then hit ENTER. Next, type ipconfig /renew and you should get a new IP address from the router.
If you have a cable modem, you may want to also renew its IP address. First, go ahead and release the IP address on the PC, then shut the computer down. Next, unplug the cable modem for a couple of minutes, then plug it back in again. Once all of the modem lights are green, power up the PC again. It should automatically renew its IP at boot.
Note: If you have a router, you’ll want to unplug it, as well, then plug it back in AFTER you plug in the modem, but before you power up the PC. The router will need to supply the PC with a new IP address.
Even without hard rebooting your router you may easily reboot it if you are able to log into it. For logging into the router control pannel..simply type 192.168.1.1 or 192.168.100.1 [depends on router too] and enter the user name and password which is genarally common [admin, password etc]. simplly click on reboot modem option and you are done