First, you might want to check that your DNS is actually setup correctly. From a different computer, use nslookup to do a DNS lookup like so:
nslookup hostname.domain.tld
Does it return the correct address for your VPS? If so, that's a good sign - the FQDN that you are using for your site is resolving correctly.
If the DNS is resolving correctly, then the next step to troubleshoot would be to see if your web server is responding to HTTP requests, by using telnet to attempt a connection to your web server on port 80. The following blog has a good write-up about how to do this: http://blog.tonycode.com/tech-stuff/http-notes/making-http-requests-via-telnet
Once you've isolated the problem to either a DNS issue or a webserver issue, you can troubleshoot further. If you post your results to these tests here, someone here will be able to suggest the next steps.