Please read this topic first:
https://forum.nostalrius.org/viewtopic.php?f=45&t=5359.
You can simply check if it's related to the account by creating a new one with one character and try to play it and see if there will be any DCs.
If there're no DCs login your main account and change the password by going into an instance and type /say .account password $old_password $new_password $new_password (You should definitely go into an instance in order to not to show the new password anyone near you!)
If there're DCs when you logged in the new account try to check your Internet connection: open Command Prompt (cmd.exe) and type ping google.com -t and look at if there any lost packets (you can do it for a while then press Ctrl+C and look at Packets Lost summary). Open
http://speedtest.net and check your connection speed.
Try to remove all of your addons (Interface), its settings (WTF) and cache data (WDB) by completely removing the following folders: Interface, WTF, WDB. (Don't forget to backup Interface and WDB folders if you need to restore them later!)
Try to download Nostalrius Installer and reinstall the game from scratch:
http://forum.nostalrius.org/viewtopic.php?f=6&t=638.
Try to install the client on another computer/laptop if you have it and test on it.