OK
If you know how to use PING, try
PING auctiva.com
I just did, and it resolved to 38.102.35.18
If you browse 38.102.35.18, do you get the Auctiva home page, i.e. type in 38.102.35.18 on the on the browser's entry window instead of the http for auctiva.com.
If the ping doesn't resolve correctly and you can browser directly using the IP address, I'm guessing your DNS server for your ISP has a problem.
Danno