Basically a company called Perfect World bought Cryptic from Atari, so now Perfect World players can also login and play Star Trek Online. Since you're an old player, select Cryptic to login with your Cryptic account.
Also note that Cryptic and Atari discovered that someone hacked into their player database last year. In order to safeguard your account, Cryptic reset all passwords and you will have to use the "Forgot password" function to create a new login password. Sometimes, the forgot password email sent by Cryptic can land in your spam folder, so make sure you check your spam folder too.