Chosen Solution
This morning my 27” iMac (2010) when my system starts up will draw a vertical light blue lines, then the appears but picture becomes dotty, like Mac has measles suddenly! The startup of computer ends halfway in the process. Is it a graphics, backlight or what?
Sadly your GPU boards VRAM has failed. Here’s the needed steps to gain access to it iMac Intel 27" (Late 2009 or Mid 2010) Graphics Card Replacement. Getting the proper board can be difficult. Sometimes re-soldering the VRAM chips can solve this but that takes a bit of skill and access to the correct tools.
