Try entering the BIOS (when you first turn it on, look for a prompt that says press XX to enter setup and press the key indicated).... if it still does it in the BIOS it's a hardware fault.
If so and it's under grantee contact them about it.
That's the problem it's intermittent. At first I thought it was just this site but it's happened on another. It's under warranty but I thought I might get some ideas from here before getting in touch with the retailer.
Random lines across LCD screens are normally a bad connection to the screen.....
Personally I'd either do the BIOS thing above, or boot it from a Ubuntu CD/memory stick and then if it still happens a driver/OS problem is ruled out and it's time to call the warranty people.