I think he's talking about the show .hack//SIGN, as in the anime.
In which case, it's about a huge mmorpg called "The World" in which people play out their roles in virtual reality. There's a group of people who find themselves together striving towards a common goal, finding something called the Key of the Twilight, which has something to do with this one character who is at the center of everything named Tsukasa, who is a character who cannot logout of The World (trapped in a video game anyone?), and has no idea how he got there or anything about his life outside of The World.
Mind you, if the original poster is asking about the game instead, I dunno, but I assume it follows a similar plot.