If you're trying to prank someone you know, and they agree to your prank, don't even bother with batch files and the like, just play a fullscreen video without controls using MPC-HC (zip file version and a scheduled task to run once at logon that plays the video using MPC-HC though command line methods).
If you are doing it for malicious reasons or intend to actually damage a system, leave now before you incriminate yourself any more.