Is my Xbox 360 messed up, or is it just my disc's?

Sometimes ill be in the middle of an online game on Madden 08, and it will freeze...or sometimes i will be playing Gears of War, and it will say disc is unreadable...and then sometimes when i turn on my xbox this little white screen comes up, and says please put in xbox 360 game or something like that, and it has it in other languages...whats wrong