my iMac 24 won't connect to the internet

[Colin H. Green]

My iMac24 (2008 model) has suddenly developed an issue. It keeps saying that the Ethernet cable isn't connected but it is and the cable works fine with my laptop in the same location. It was working perfectly a few days ago and the problem developed overnight. Can anyone suggest a trouble shooting routine?

 

[Hermes-II-SysOp]

Colin, with that limited information, it is going to be difficult for anyone to offer you any real assistance. It would be helpful if you could provide more specific information.

For example, what kind of network configuration do you have? Do you use a cable modem or DSL line? Is your computer connected directly to it? Are you on a hardwired LAN ? Are you on a wi-fi network? Do you use a DHCP server or do you manually assign a LAN address to your machine?

Without knowing the specific details to questions such as the above, I can only offer very generic suggestions, such as:

1. Shut everything down and leave it off for a few minutes.
2. Reconnect your modem first and let it re-establish a connection with your ISP.
3. If your modem is connected to any kind of router, turn that on next. Let it establish its link to the modem.
4. Next, connect the ethernet cable between your computer and the modem or router, whichever it is.
5. Check your Network preferences pane, and make sure that all of your settings are still set properly.

I have had experiences on rare occasions where either my cable modem or my wi-fi router will become confused. If your router is set to use a built-in DHCP server, this could alter the NAT address -- internal IP address -- of the machine that you are using. This could break your Internet connection.

In fact, power fluctuations and power outages can also mess up the above. Maybe something happened during the night to mess things up. It does happen.

I hope this helps in some way.

 

[honestone]

Colin, Hermes is correct. However, most such issues seem to get resolved by following the steps Hermes states above. In most cases, I just needed to do steps 1 through 3, without disconnecting the ethernet cable. I then start up my Mac, and everything is fine. I suspect my problem was with my ISP, Comcast.

 

[Mispeltyoof]

My 27inch Mac was great with my wirlees router for a year. In the last couple of days it has decided to only connect for a minute before failing. All other devices work fine including an ancient windows laptop sitting next to it. Done all the resets etc know to man with no success . It is now a large and very expensive paperweight!

 

[honestone]

When you say "did all the resets", does that include the shut down process Hermes described in his post above?

 

[Mispeltyoof]

Yes .....3times...also followed BT advice who know about Mac software probs but are powerless. Every time I try something the problem gets worse . A week ago it cut off every ten mins now only lasts thirty secs

 

[Hermes-II-SysOp]

If after doing all of the previous steps that I outlined -- and several times no less -- your 27" iMac continues to lose its connection to your wi-fi router -- Is it an Airport Extreme or Airport Express? -- my last suggestion would be to take it in to an Apple Store or an authorized Apple reseller in your area. If your iMac is still under warranty -- yes, it is expensive, but well worth it, I recently discovered -- it won't cost you a penny for parts or labor to have it fixed.

However, at this point, if your iMac continues to work fine, other than losing its wi-fi connection, I am not convinced that it is a hardware issue. I still suspect that something is messed up somewhere in your settings.

Have you considered corrupted prefs files?

Maybe if you delete whichever prefs files apply to your particular situation, and start fresh with new settings via the Airport Utility app and Network prefs pane, you will be able to resolve your problems.

 

[Mispeltyoof]

also downloaded 10,10,2 which did absolutely nothing. Took thirty five minutes as kept switching off contact with router very coup;e of minutes...beginning to wish I gone with a PC now ...this iMac is expensive crap!

If after doing all of the previous steps that I outlined -- and several times no less -- your 27" iMac continues to lose its connection to your wi-fi router -- Is it an Airport Extreme or Airport Express? -- my last suggestion would be to take it in to an Apple Store or an authorized Apple reseller in your area. If your iMac is still under warranty -- yes, it is expensive, but well worth it, I recently discovered -- it won't cost you a penny for parts or labor to have it fixed.

However, at this point, if your iMac continues to work fine, other than losing its wi-fi connection, I am not convinced that it is a hardware issue. I still suspect that something is messed up somewhere in your settings.

Have you considered corrupted prefs files?

Maybe if you delete whichever prefs files apply to your particular situation, and start fresh with new settings via the Airport Utility app and Network prefs pane, you will be able to resolve your problems.

Thanks for all your help. Everything appears in order but my online connection is worsening by the minute have to keep turning wifi on and off just to get this reply typed. .Will try to find the airport utility (never heard of it) but can't connect long enough to get to app store. All other devices work perfectly (windows and iPad,phone etc) Wi fi works for a very short period every time I turn it off then immediately on again. So frustrated going to purchase an iunfeasibly long ethrenet cable and try that. This is driving me mad! But once again thank you

 

[honestone]

First of all, you should already have the AirPort Utility application. It is located within the Utilities folder, which is contained in your Applications folder.

Secondly, that only works with an AirPort Extreme Base Station, AirPort Express, or AirPort Time Capsule. If you have another kind of router, that won't help you. This link tells you how to use that app:

https://support.apple.com/kb/PH18561?locale=en_US

Third, it is probably best to follow Hermes' advice about deleting the preference files that apply to your setup, then proceed with setting up your router and Network preferences.

 

[Hermes-II-SysOp]

You know, if trashing your prefs files and starting fresh with new settings doesn't resolve your problem, another possibility -- which I mentioned in my very first comment to you -- is that there may be a NAT address conflict occurring between the different devices which are connected to your wi-fi router.

That is why I advise you to take a good look at the current settings for EACH of the machines that use your router. As I already stated, you need to look at the Network prefs pane on each device -- at least on your Macintosh machines; I don't know what Windows machines have -- as well as your base station setup -- assuming it is an Apple router -- via the Airport Utility app.

The fact that you keep turning your wi-fi router on and off hints at the possibility that there may be such an internal IP address conflict occurring.

More specifically, if on some of your devices you have manually set an internal IP address, while on others you have the machine set to accept a dynamic IP address from the DHCP server that is in your router, that may cause you the kind of issues that you are now experiencing.

That could possibly explain why you meet with partial success each time that you turn your wi-fi router on and off.

In short, you need to make certain that all of the devices in your LAN are on the same page. Personally, I would consider manually setting a NAT IP address on all of them. That way you can be certain that there will be no such conflict occurring between them.