10 steps to fix a broken Internet connection
1. Try another website or service
If you're using a web browser, try navigating to another site to make sure the problem isn't specific to one website. If that doesn't help, try a different browser. If you're using a service like Twitter or iTunes, go to a web browser and try and navigate to macworld.co.uk (say).
2. Use WiFi
Check that you're on the right network. OS X and iOS are generally very good at connecting to the 'right' network, usually the one operated by the modem/router connected to your ISP's broadband network. But they're not perfect. If, for example, you have a BT Home Hub, you might find it connects to the 'BT Wi-Fi' or 'BT Wi-Fi with FON' access points instead of your home wifi network. Click on the Wifi menu in the Mac's menu bar and check which network has a tick next to it. If it's not the right one, select the correct network.
On and iPhone or iPad, go to Settings and Wi-Fi to check. (Read: How to adjust settings on an iPhone)
Read: How to manage Macs on a Windows based network
3. Is it the network or the device
If you can't access the Internet on your Mac, check whether another device, say an iPad, can connect. If the second device can connect, the problem is with your Mac and not the router or broadband connection. If the problem is with an iPad, try connecting from your Mac.
Read: How to troubleshoot Mac WiFi problems
4. Turn it off and then on again
It's cliched advice, but it's a cliche for a reason: it works. If your Mac is displaying an exclamation mark over its wifi menu bar item, click the menu and select 'Turn Wi-Fi off.' Wait a few seconds, then turn it on again. Sometimes this is all it takes to fix a wifi problem.
If the problem is with an iOS device, go to Settings, then Wi-Fi and move the slider to the off position. Wait a few seconds, switch it back on again, and then try connecting again.
5. Restart your router
If you've eliminated all of the above, the next step is to restart your router. It's remarkable how many problems can be fixed this way. Even if the status lights on the front of the router show that it's connected, it's worth restarting. You can do it either by pressing the power button, waiting ten seconds, and then pressing it again, or by pulling the plug out, waiting, and then plugging it back in again. You'll have to wait for a minute or so until it resets itself and re-connects. Once it's done that, try and connect to the Internet again.
Read: Which WiFi router is best for a Mac
6. Network diagnostics
Your Mac has a built-in tool for diagnosing connection problems, but, like many of OS X's useful tools, it's tucked away. To access it, click System Preferences in the Apple menu and click on the Network pane. At the bottom of the window, click Assist Me. On the next dialog box, click Diagnostics. You'll now be taken through a series of steps; the first will ask you to choose how you connect to the network. If you choose Wi-Fi, you'll then be asked to choose which wifi network you want to connect to. The utility will then perform a series of tests to try and identify where the problem lies. Sometimes it will be able to fix it, on other occasions it will tell you where the problem is, but won't be able to resolve it.
7. DNS
If none of 1-6, above, work, it's worth changing the Domain Name Server (DNS) settings. The DNS settings dictate where your Mac or iOS device goes to look up a URL and turn it into an IP address. If there's a problem with the DNS server, it won't be able to resolve URLs and so your Mac won't know where to go to find a website or online service. If you've never changed DNS settings, they'll be set at the the default used by your ISP. And so if your ISP has DNS issues, you'll have connection problems.
To test whether you have a DNS problem, open a web browser and type http://74.125.224.72/ into its address bar. That should take you to google.com. If it does, and you can't access Google by typing 'google.com' into the address bar, it's a DNS problem.
To fix it on your Mac, go to the Network pane in System Preferences again. Click Advanced, then click the DNS tab. Click on each of the servers in the left hand window and click the '-' button at the bottom. Now replace them with either DNS servers run by Open DNS (208.67.222.220 and 208.67.222.222) or Google (8.8.8.8 and 8.8.4.4). Both are free to use and very robust.
You can do the same on an iOS device by going to Settings, then Wi-Fi and clicking on the 'i' next to your wifi network. Then type the new DNS server address.
Read: What you can do with System Preferences on a Mac
8. If some sites work but others don't
Occasionally connection issues crop up with several websites, but not all. On these occasions, out of date cached files may be to blame. The solution is to flush the browser's cache. The method will depend on your browser. In Safari 8, go to the Safari menu and select Clear History and Website Data, then choose 'all history' from the menu. Note that this will delete your History on the Mac, and, if it's signed into your iCloud account, all other devices signed into that account.
Read: How to clear your Safari history and cache on a Mac
9. Connect directly to your router
If you know the IP address for your router's admin page, type that into the address bar in a browser window. If you don't, it should be in the manual. Log in to the router with your username and password and look for the troubleshooting section. There should be guidance there, or a diagnostic process which should help identify whether the problem is on your network or your ISP's.
10. Contact you broadband provider
If all else fails, it's probably because there's a fault in your broadband provider's network. They should have a status page on their website advising where there are problems. If you can, navigate to that from a phone with a mobile internet connection and check. Otherwise, call the helpline number and choose the option which takes you to the automated service which advises of local connection problems. If there's nothing reported, you can either wait and try again or steel yourself and join the queue to speak to someone and report the problem yourself. Good luck.
Also read:
What Automator can do for you and Automator Workflows
How to troubleshoot WiFi problems
How to show hidden files and folders in OS X
How to generate SSH keys in Mac OS X