One way to know if you site is running is to use a third-party solution. There are many companies that will check your site, some are free. 2 that are good are: www.internetseer.com and www.watchmouse.com. Both offer limited free services, checking your site every few hours, sending you an email when it goes down.
Another solution is if you have a computer connected to the Internet most of the time, use a shareware program on that, including: virdi-software.com ‘s eyeonsite (freeware) and Robomagic.com’s sitec (shareware).
So, now, if your site goes down, what do you do? Before you contact your website hosting company, make sure the problem isn’t on your end, something wrong with your computer or your ISP. Is your computer connected correctly to the Internet? Can you see other sites? Is it just a temporary problem? Is it only 1 page or the entire site?
Try a proxy site to see what your site looks like to others:: www.anybrowser.com‘s site viewer is a great way to check if the site’s up, AND, to see what the site looks like to older browsers — you may be shocked!!
If the site really is down and it’s been a while, contact your hosting company and explain it to them. Good luck! 🙂