I have an Early 2009 24” iMac (Model # A 1225, dual core Intel, running 10.6.8) and it still works great. But in the past few months it’s developed screen anomalies. First, a very thin white line appeared horizontally right above my (bottomed) dock. Then two more such lines, showed up, just above the first one. More recently four horizontal bands have appeared, not of color but just shading of what’s on the screen; these are of equal depth and are each darker as they go down the screen. The bands are prominent when the screen just wakes up, but completely disappear after several minutes. The thin white lines are always there and sometimes become multi-colored along their lengths. I ran a recommended test of doing screen captures and neither the bands nor the thin lines appear in the captures. I understand this may indicate that it’s “only” a display problem and not a more serious graphics card or GPU problem. I zapped the PRAM and SMC but they had no effect. (I did not try Safe Mode.) Anyone care to hazard a diagnosis? A prognosis? Are there other tests I can try?