Why does my computer screen bounce up and down sometimes?

Name of an old computer game?

• im looking for a computer game i used to play. it was really simple, u had 2 red and white balls that bounce around the screen and you used your cursor to build horizontal and vertical walls to separate the balls and put them in smaller and smaller spaces. then you go to the next level that has 3 balls, and then 4, etc. if u know the name of it please help.

• Answer:

  It's called Jezzball! Haven't played it for a while, but it's a fun game.