Before raising the alarm, do a check to find out if the website is really down by testing the link at http://downforeveryoneorjustme.com/
Check these useful sites and links to diagnose website down issues in order to arm ourselves with enough information to ask hosting providers to do something about it when they aren’t being very helpful.
1) Smashing Magazine step-by-step guide:
http://www.smashingmagazine.com/2010/12/13/what-to-do-when-your-website-goes-down/
2) Hostgator detailed a good explanation and useful links to 2 free online network tools to aid in dianostics:
http://support.hostgator.com/articles/hosting-guide/lets-get-started/dns-name-servers/where-can-i-view-if-my-name-servers-were-setup-correctly-and-what-ips-they-currently-use
3) Online tools
Leaf DNS http://leafdns.com/
Network-Tools.com (for advanced users) http://network-tools.com/
4) VirusTotal
Created by the guys at Google, an online too that checks for virus that may have brought down the website.
https://www.virustotal.com/en/