By: fairytale of los angeles

Could Be the logic sheet yet again-- my 15" MBP did nearly the said thing when the graphics chip finally died (a known issue).

The Apple Store staff have a special HD they exploit to check for exactly that problem. The minute you utter "weird blocks and lines on the screen," they'll know what to stare all for.

Source: http://ask.metafilter.com/171115/Scary-pixelated-laptop-displaywhat-should-I-do-next#2461903