Need help with my computer screen!?

Every time I use my laptop computer the screen completely stuffs up, any white background turns purple and things like pictures have random green lines all over them, and it's really annoying me! I desperately need my computer for work, and while it's useable, I'd really rather have the screen stop doing this... I can't do anything like watch youtube, and sometimes it's hard to read what it says. It's a HP Pavilion zt3000 laptop, if anyone could help me that'd be wonderful.