Sorry, I forgot to finish my sentance. XD You weren't supposed to put in a code. Just starting the program tricks the game to work if you downloaded it in full.
I agree it is very frustrating... Where did you download the game from, anyway? Was it through a Torrent?
Also, about Aoba, Virus and Trip... It seems you haven't played far enough into the first DMMd, as it's all explained there. Admittedly, in the TRUE story endings (After you 100% complete Kojaku, Noiz, Mink and Clear's route, a last one will open up for you to play)
However, if you're SERIOUSLY interested, and don't mind being spoiled, here are the answers you seek. I will not go into too much detail, as the story really explains it very well, so I will be brief.
There. I kept out the juicy details, but if the first DMMd works for you, you should really finish that game first before DMMd Reconnect anyway.