You may have "Autorun" turned off. If this is the case, go into your Windows Explorer, select the Disc Drive, find the X Plane executable file and double click it. I know you said you got a new x plane disc, but check the disc anyway for scratches, dirt, smudges, etc... You may also have dirt or dust inside the disc drive. Give it a good blow inside the drive or even better, get a can of compressed air and use that.