Running MAC 10.6.8 wireless for 3 years.

Reboot your home router. (Power Cycle the router)

Give your System Preferences -> Network -> WiFi -> Advanced -> TCP/IP -> DHCP Client ID -> aSimpleUniqueValue

Do the same for Ethernet -> TCP/IP -> DHCP Client ID.

Some home routers do not play nice with Macs and managed to give out all their DHCP IP addresses forgetting that it was the same Mac that was making the request. Sometimes giving the Mac a DHCP Client ID keeps the router "Sane". Rebooting the router is a way to get it to reset all its DHCP leases.

The DHCP Client ID as circled in the screen shot below:

As you can see from the screen shot, my DHCP Client ID is a simple string that within my home uniquely identifies my Macbook Pro from my Mac mini, from my Wife's Macbook Air, not to mention the iPhones, iPads, and iPod Touches that are on the home network.

NOTE: I give my WiFi and Ethernet TCP/IP settings the "Same" DHCP Client ID, as it is perfectly OK for the DHCP Server to give the same IP address to both your WiFi and Ethernet interfaces, and if you switch from WiFi to Ethernet in the middle of some network operation, the Mac will transparently switch interfaces without loosing the connection because both interfaces are using the same IP address, and the remote destination will not know a thing about your switching networking interfaces.

Many DHCP servers in home routers will use the DHCP Client ID to reassign the same IP address to a device, and not keep giving out new addresses until it runs out of IP addresses. Once a DHCP server has given out an IP address there is a lease time associated with the address, and the server will not give out that address again until the lease time expires, or the server is rebooted (power cycled).

Also remember to reboot (power cycle) your home router, as that is the device running the DHCP server and assigning IP addresses.

Now my ideas are just shooting in the dark, so do not assume I know what I'm talking about 🙂

Please try booting your Mac into "Safe" mode

<http://support.apple.com/kb/ht1564>

This will eliminate any 3rd party interference, such as an aggressive anti-virus package (which are totally NOT needed anyway). Safe mode does not load 3rd party extensions, and does not run "Startup Items", etc... So if a 3rd party package is interfering, Safe mode is an easy way to test without those packages loaded.

If you have WiFi, can you try using that to get an IP address?

Have you tried a different Ethernet cable. Maybe borrow one that you know works, such as one from the internet phone setups. While Ethernet cables do not go bad by themselves, cats, dogs, kids, humidity, or other environmental stuff might cause the cable to fail.

Is it possible to connect directly to the modem, bypassing the router (NOTE: some cable modems lock into the first device they see after being powered up, so you may need to power cycle the modem if you are going to try attaching your Mac directly to the modem, and power cycle it again, when putting the router back as the connected device).

You could try manually assigning your own IP address. I do not recommend this, unless that Mac does not leave the house (if it is a laptop that leave the house, a fixed IP address will cause problems when you attach to another network). You would look look at your router's IP addresses, and look at what the DHCP address range was on your router, and choose and address just outside the DHCP range (for example, if the router was using 192.168.1.2 thru 192.168.1.100 for its DHCP range, you could choose 192.168.1.101 (where different routers using different non-routing IP addresses; common are: 192.168.0.*, 192.168.1.*, 192.168.2.*, 10.0.0.* are the ones I've most commonly seen; you must figure out what your router uses).

There are two things you can try:

First, make sure you know the name of your wireless router and the password to connect to it. Write these down somewhere safe.

Open Network Preferences. Select your WiFi on the left. Select Advanced at the bottom right.

In the list under Network Name, select and delete your router. The "-" button will delete it. This is erasing your router from the list that your computer remembers.

Close Network Preferences.

Now reopen Network Preferences and get back to that list under Network Name. With the "+" button, add back your router, choose the correct security protocol, and enter the password to connect. See if that gets you back on the network and the internet.

A second method, more severe perhaps, is to open your Keychain Access utility, and either under the login or under the system keychain lists, find the item for your router name and delete it. It may show up multiple times or under multiple keychains, delete all that have the name of your router. Exit Keychain Access. Then, repeat the removal of the router from Network Preferences as described above. Then reopen Network Preferences and choose and login to your router and try again. These steps basically erase all knowledge of the router and its setup from your Mac and make it start all over with a fresh connection and login. Something appears to be incorrectly configured and this erases the configuration and starts with a new one.

It's hard to tell from your posts, so I'll ask:

Are you logged in correctly and connected to your router via wireless? That would have happened when you select your router by name and then log in. Does the wireless (Wi-Fi) icon at the top right of your screen show a check mark by your router?

Here is another important diagnostic: log in to your Mac as another user (create a new user if you have to). Can that user connect to the router and to the internet?

haydad65 wrote:

Does the wireless (Wi-Fi) icon at the top right of your screen show a check mark by your router? There is a Icon there but it is grayed out with an Exclamation Mark in it.

Logged in under another account name, which hasn't been used in two or more years, and the same Grayed out Icon with the Exclamation Point mentioned above.

When the WiFi icon shows that exclamation point it means that you are not connected to your (or any) router via wireless. In fact the wireless icon should show solid WiFi bars (they resemble radio waves emanating up from an antenna) when you are connected to your router even if the router has not on the internet.

Click once on the WIFi symbol that is grayed out and has the exclamation point. You should see:

"WiFi: On" or "WiFi: Looking for Networks"

and also below that should be a list of routers that your computer can see wirelessly. This list should include your router. If you were connected to it, there would be a check mark by it. If you see your router name without the check mark, select it. If you don't see your router name, then select

"Join Other Network" and then enter the name of your router, select the proper security protocol (most likely WPA2, but you need to select the precise correct one) and enter the password. If you don't enter the exact name of your router or if you don't select the specific security protocol or if you don't enter the right password, you won't be connected to the router, which results in that exclamation mark on the WiFi icon.

To go much further in troubleshooting, you need to indicate the name/make/model of your router. Most routers in the U.S. will work with Macs if in the Network Preferences pane, selecting WiFi and selecting the Advanced button, for the TCP/IP button you should have only

Configure IPv4: Using DHCP

and if it shows Configure IPv6 that should have "Automatically" with nothing else there filled in; DNS settings depend on your internet provider and I wouldn't touch any of the other settings.

I think your basic problem is that you are not connected wirelessly to your router. That's the very first problem to solve, hopefully as indicated above.