My diamond wont start up

Wen i put my diamond in it says play game on the lower screen and the on the upper screen it says 'The data could not be read...please turn off power and the remove and reinsert the DS game car'. This is really weird because it hapened right after I turned it off like 5 minutes ago. So i started playing it again and it showed me that stuff. But i never took out my game so it couldn't of got scratched. I Look over it and everything looked fine. Does any 1 have the same problem, Cause i need help. Ive beat the whole game and got the final regi. I dnt want to lose my progress