There are a number of reasons why this may be the case. First, depending on the TTL ("time to live") setting for your DNS records, it could be that the DNS change just hasn't propagated yet (your browser is still looking for the site at the old IP address, since that's still cached in the DNS server it's accessing).
If the site is loading from another device (like your phone, or a co-worker's computer), you might try clearing your browser cache, or even re-booting your computer. This re-boot has been required for a few clients reporting that clearing the browser cache was not helping.
If no one in your office can access the site (yet it can be accessed from computers/devices outside your internal company network), check with your IT team on whether you have a firewall or DNS setting on your internal network that needs to be updated or cleared.