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"