When a website stops working

Yesterday the site loaded. Today it shows an error, or a blank page. Work through these checks in order, because each one points to a different person who can put it right.

1. Your device, or the site?

Google's Chrome help suggests checking whether the problem affects one website or several. If several sites fail, its advice is to check your internet connection.

If only your site fails, try it on a phone using mobile data. A site that fails everywhere has a fault of its own.

2. Has the domain name run out?

ICANN's lookup tool shows who your registrar is, in its "Registrar" field. The registrar is who renews the name.

Nominet's published timetable for .uk names runs in stages. Through the 30 days that follow the expiry date, the name works as normal, and renewal is still open. Between day 30 and day 90 the name stops resolving, while renewal stays open. Once 90 days have passed, renewal closes and the name drops five days later.

Who to contact: your registrar.

3. Has the hosting stopped?

Hosting can be a separate account from the domain. In the NCSC's list of important accounts, domain hosting has an entry of its own where it is kept separately. Look for messages from the host about a failed payment or an expired card.

Who to contact: your hosting company.

4. Has a setting changed?

Google's list of Chrome errors says ERR_NAME_NOT_RESOLVED appears when the address no longer exists, or now points to a different IP address. A recent change to the domain's settings can cause it, as can a lapsed name.

Who to contact: whoever last changed the domain's settings, or your registrar.

5. Is there a certificate warning?

Chrome lists "Your connection is not private" and "SSL certificate error" among its certificate errors. For a date error (NET::ERR_CERT_DATE_INVALID), Chrome's help tells visitors to check that their device's date and time are right.

If every device shows the warning, the site's certificate is the next thing to look at.

Who to contact: your hosting company, or whoever set up the secure connection.

6. Has the site been hacked?

Google Search Console has a Security issues report. It lists what Google found if a Google evaluation determines that your site was hacked.

The NCSC's recovery guide starts with contacting the account provider and following its recovery steps. If you have lost money, it says to tell your bank and report it to Report Fraud, or, in Scotland, to contact Police Scotland on 101.

The NCSC also runs a line for live attacks. A business, charity or other organisation currently suffering a live cyber attack (in progress) should call 0300 123 2040, which answers at any hour, every day of the week.

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