My computer shut down by himeself when i trie to play with a simple game and sometime even whan i trie to watch films my computer is acer L100

your computer must be overheating. itunes, reapPlayer, windows media player, and the likes require a lot of processing power to decompress and decode files, which can cause the system to get hot and some systems shut down automatically when the temperature reaches an unsafe level.you can try to clean the fins on the heat sink that sits under the cpu. when they collect dust it restricts the airflow and prevents proper cooling. but if this does not resolve your concern, it could be that overheating is not the main problem. it could be a bad memory. you can try to open your cpu and remove/replace one RAM unit and check if that'll solve your problem. if not, you can try to test all the RAM sticks that you have to determine the culprit.

hope this'll help you

ciao!