Hey, welcome back. This isn't an official answer.
No one can help you with your old CD Keys or Bioware password, but on the bright side, you shouldn't need either of them! What you do need is:
a) Bioware user name that went with the character you are trying to get back, or to create a new character. The latter might be easiest all around, honestly, for trying to get used to things again. A huge amount of time has passed IG too, so it's kinda awkward playing a human who was around since Blood, as they'll be centuries old by the default timeline. Nobody's gonna stop you, though (and you wouldn't be alone)! If you don't remember the username at all, Dorg would be the one to answer what the possibilities are if any and what information would be needed, sorry.
b) If you got the new game from GOG, you will need to email them asking for a multiplayer-compatible CD Key. The one that comes with purchase is not unique, and so anyone who got their game from GOG and did not do this will be competing for the same key on our server. For that matter, anyone reading this who hasn't already done this here should as well, it's free and you won't be blocking others who haven't gotten theirs from playing online.
I suggest you still look around and thumb through information about the place that might be different since you were here, last!