There can be a few reasons for this issue, the top two in our experience are unexpected changes to your router configuration or your hosting provider has blocked your IP address.
The latter is more likely if only you, and anyone on the same WiFi network as you, suddenly loses access to your site or sites that are hosted by the same company. This can be a automatic trigger resulting in some event that the system interpreted as an attack – something like a lot of people logging in using the same username or password.
Usually the hosting service will block your ip address for a short period of time, usually an hour. If you find this is the case, contact your hosting provider and ask them for advice on how to avoid this issue in the future. The good news is the the rest of the word can still see your site, your hosting provider is just looking out for you!