How long has it been since you made a change effecting DNS? DNS changes do take time to propagate.... anywhere from a few minutes to 72 hours with the average being about 8 hours. Also the changes happan at a different time for each DNS server (and there are 1000's around the world).
whatsmydns.net gives you a tool to watch the progress. Note tho that while they have a few dozen key points identified on the map that it doesn't actually represent every server in the world.
In the dreamhost panel if you go to the domains DNS page, there should be a refresh button you can click as well that might help.
You can also post the domain name here, that gives us the ability to use tools like whatsmydns.net to give you a more specific answer.