Video And 3D game glitch

[darkjoker]

ok.so i've recently downloaded a computer game.yet eveyrtime i get on and play, it just randomly stops and ends..this also happens when i watch videos in fullscreen. i am really tired of this...is there possibly a glitch or virus in my computer?. if it's more likely a possible virus please inform me with low cost/dependable software it's been like this for months.