Windows Vista Errors - Unexpected System Failures

Hello My name is Leo Maneke, and i just bought Microsoft Windows Vista Home
Basic, and i like this new version of windows. When i installed it and first
starting running it i had no problems with it then i started installing my
programs, putting my pictures and music on it, and sometimes when I run
Windows Media Player, or a game like Super DX-Ball Deluxe, the computer will
shut off then restart, because it didnt recover when it came out of full
screen mode. Can you tell me why it will bring up the blue screen and
restarting unexpectedly? i'm hoping that the system isnt failing on me
already. Your input will be very appreciated and will help me make my system
run more efficiently. Thank you for your time.