I've been somewhat annoyed with all of the responses to this thread. Anytime you have a device that's not being assigned an IP address, the following steps should be taken (Windows specific):
edit: You really don't even need to release and renew if you still have the lease you had when you lost connectivity. You're better off a) verifying that your cable/DSL bridge (modem) still has connectivity, and then connecting to your router/firewall (assuming your using one) and having it do a release/renew. If you can't ping your gateway, reboot your router/firewall and try again.
1. Ensure that the device has physical connectivity.
2. Perform an ipconfig/release
3. Perform an ipconfig/renew
4. Assuming failure, STATICALLY ASSIGN THE IP ADDRESS to a known free IP address, or the one you previously had and attempt to PING A) the gateway, B) the DHCP server.
5. If you cannot reach the gateway, troubleshoot the gateway. This could involve power cycling your router/firewall or your cable/DSL bridge (modem) (see below), or moving to an alternate port on your router/firewall/AP.
6. If you can reach the gateway, verify that the gateway is responding to ARP requests, by checking your ARP cache and verifying that you're learning the gateway's MAC to IP address information.
7. If you can reach the gateway but not the DHCP server, troubleshoot the server.
8. If you're directly connected to your ISP with no firewall/router (you're a fool) and you've reached this step, work with your ISP to resolve this issue. If you're behind a firewall/router/AP, proceed.
8. In many home environments, where you're using a router/firewall/AP or some combination thereof, the gateway and the DHCP server are one in the same. Power cycling this device and/or verifying it's configuration is the best option.
Finally, if your firewall/router is providing your home devices with IP information, but it is not receiving a DHCP lease from your ISP:
1. Have your firewall/router do whatever is the equivalent of a release/renew.
2. If that does not resolve the issue, power cycle your DSL/Cable bridge (modem), and then the router/firewall AP. The idea is to have the cable/DSL bridge totally rebooted prior to the firewall/router rebooting. Your cable/DSL must be in a connected state for your router/firewall to get an IP address from your ISP, and your router/firewall must have an IP address from your ISP for you to reach the Internet. When everything comes back up, connect into your firewall/router/AP. If it's assigned an IP address from your ISP, you're done, if not, call your ISP and resolve the issue with them.
Sorry, but some of the responses to this thread have been a bit on the drastic side for such a relatively simple issue.
Things you should not be doing as initial steps:
- Reboot your PC
- Swap NIC cards
- Connect directly to your DSL/Cable modem. Once you do this, you're computer is effectively unprotected. Yes this is a valid troubleshooting technique, but more of a last resort.
The most likely reasons for you to lose network connectivity to the Internet:
- Your DSL/Cable connection dropped
- Your DSL/Cable modem was somehow reset
- Your Router/Firewall/AP reset or somehow lost its configuration
- Your wireless signal was interrupted
- Your cable is shitty and caused a loss of connection cause you bumped it
- Your NIC failed (this really doesn't happen that often folks)