There’s no point spending lots of time on online marketing for your website, if your website isn’t there! This can be caused by a number of reasons – mainly based around hosting and domain name issues. Website hosting, particularly on shared servers, isn’t 100% reliable. Many guarantee 99.9% availability, which seems high, but that can mean your site is unavailable for up to 9 hours over a year.
To keep an eye on things you can use a free tool like that offered by pingdom.com (free to monitor one website). A great tool to use alongside Google Alerts (see post: Use Google Alerts to improve your SEO) this one can keep an eye on your website and warn you if it becomes unavailable. It works by ‘pinging’ your website regularly, (a ping is an internet process of just asking a server if it is there – a bit like a sonar ping, which is where the term comes from I guess), and warning you if it doesn’t get a response after a few repeated attempts. It will also tell you when your site comes back up again.
If your site goes down for longer than reasonable then contact your web host and find out what is going wrong. If it happens regularly then change your web host!