There are several possibilities as to why you cannot reach DirectAdmin (anymore). Please check whether one of the below causes applies to you.
1. Did your domain just become active?
If you just registered your domain, moved it or awaiting a moving, then it might be that DirectAdmin is not reachable through your domain name. You can then use the single sign on option through the partner platform.
2. Are you using a firewall?
Some firewalls are blocking ports 2222 and/or 2223 (and usually then also all numbers above 1023), which makes DirectAdmin unreachable. Configure your firewall in such a way that TCP-ports 2222 and 2223 for all outgoing traffic are accepted.
Do note that you may be behind several firewalls. A lot of operating systems have firewalls built in, you may have installed a software based firewall and it might be that you are behind a hardware firewall (for example in your router).
Through https://portforward.com you can find more information on how to open ports on your router.
3. Is your domain suspended?
You can check this by visiting your website. Is your website not visible and is your domain no longer active, then DirectAdmin is also no longer reachable through your domain.
4. Is your website still visible?
If not, it might mean that the server is down, or your domain has moved away.