Sometime hosting companies block IPs they could of blocked yours on accident? One of my lame hosting companies did it and I sent an email and they fixed it.
Send your hosting provider an email about the problem.
Two solutions if you have a DNS problem:
1. Go to a online proxy and type the URL and see if it loads
2. open cmd.exe (windows) ipconfig/flushdns (this only updates to your ISP's latest, might not work)