may be like rousp said the fans are not working or u need to take it apart an use some computer cleaner,duster,my old 360 did that it was the xenon chip now i have the falcon chip one it works well but the disc tray wont open some times i have to use contact cleaner on it but a few days later same prob i tap on the top to get it open,good luck there a pain to take apart all the screws an the removal of top an bottoms a pain it takes time an some skill.
j Update: just take 360 apart clean laser with clean Q-TIP an alcohol that will clean dirt or any stuff off the laser it worked for me dont tighten screws to tight when putting together disc tray wont open clean the system when you open it ok good luck.