Hello! I have iMac Early 2008 with 20inch screen- So i have a question i have Radeon HD2400XT 128MB and i have feeling that the gpu in dying (light vertical lines)...I have Yosemite 10.10. Can i replace the gpu with better or existing one (working)? Is this a hard or easy job? Where i can find any tutorial? Lines: Is this screen or gpu problem? Thanks in Advance im new on this forum and this is my first Mac! Best Regards!