I see a lot of topics created regarding this issue. Please allow up to 48 hours after updating your nameservers before worrying why your website is not resolving. Nameservers need to fully propagate throughout the internet which takes up to 48 hours. If your site is not resolving after this time you can try clearing your cache or trying a different browser to check your site. If the site is still not resolving then there may be another issue and you'll want to contact the community for assistance.
All great tips @justingodfrey. If I could add one (albeit not common), another thing to check is whether or not your domain has DS records in its DNS. If you have a domain that is using GoDaddy nameservers and have DS records set for the domain, this can cause propagation to halt or occur sporadically.