That is correct, it is indeed an iMac with a graphics card issue! When graphics cards start having issues it can look like this iMac. One of the most common issues that occurs with a failed graphics card is the computer booting to a white screen. The Apple logo comes up, the progress bar goes across, then it goes to a white screen and just stops.
These symptoms aren’t always the graphics card, so be sure to bring it in for a free diagnosis!