Apple has begun a graphics card replacement program for select mid-2011 iMac configurations, after determining that the graphics cards in some 2011 iMacs may fail.
On its support webpage, Apple says that some AMD Radeon HD 6970M video card used in 27in iMacs with 3.1GHz quad-core Intel Core i5 or 3.4GHz quad-core Intel Core i7 processors may fail.
The graphics card failure in these models can cause "the computer's display to appear distorted, white or blue with vertical lines, or to turn back," Apple says.
The affected iMacs were sold between May 2011 and October 2012.
Customers with applicable iMacs that are experiencing these symptoms can set up an appointment with a Genius in an Apple Retail Store to have their iMac evaluated, or can go to an Apple Authorised Service Provider. Alternatively, customers can call Apple Technical support.
If Apple determines that your iMac meets the requirements, it will replace the AMD card free of charge within three years of the iMac's original purchase date.
Plus, Apple also says that customers who have already paid for a repair or replacement of their graphics card after experiencing these symptoms in an eligible iMac could be entitled to a refund.