After a playthrough of Mass Effect is completed, that profile can be played again. When you have finished with the final boss and ended the game, go to "New Game" and go through the process once more until the "Select Existing Profile" option is available to you. This should be before you select whether you want a default Shepard or a custom Shepard. From there, select the profile you had used before to initiate a second playthrough. All of your weapons, supplies, and talents are carried over. Sometimes it takes more than two playthroughs on one profile to reach level sixty. Just keep playing until you get it.