Lets see.Your account take D/C maybe coz you have to low internet connection.As Titan sayed use double click when you select a character.If you are inGame and you use the vault and you take D/C when you put the scroll on specific item,then sell it at the shop cuz is dupe.If isn't anything above that i said try to reinstall the game and let us to know if the problem still continue...
If you have a good connection and don't hit enter upon login then the possible reasons might be:
1.In the firewall the main.exe is not an exception and the firewall enters it up like an error and you get DC.Check the firewall and add the exe as an exception.
2.You are trying to load multiple programs while loading the main.exe.Close everything and then load the exe.
It is possible that the antivirus program you're using detects the main exe. and shuts it down.Check the program for any logs and try to put an exception marker,in the program not to check or scan the folder with the game.