Recently my IP address was blacklisted by directadmin on my own server. Here's a how-to that may save you time, in case you're unable to login to DirectAdmin.
Start DirectAdmin in debug mode
cd /usr/local/directadmin killall -9 directadmin ./directadmin b2000
Now try to log into directadmin. You should see the reason why you are unable to. For me it was "Blocking blacklisted IP xxx.xx.xxx.xxx"
Debug mode. Level 2000 DirectAdmin 1.45.2 Accepting Connections on port 2222 Blocking blacklisted IP 184.108.40.206
Remove your IP address from DirectAdmin blacklist
Add your IP address to DirectAdmin whitelist
Now Restart directadmin
service directadmin restart