Blue and yellow spots all over my screen?

I have a lat 2009 27" iMac and have been using it with 8gb of ram for years. Last week I purchased 16gb form OWC took out the original ram and put in 4 new 4gb sticks. Within 3 hours I suddenly began to see blue and yellow 1/4" "spots" on the screen. They gradually spread and finally froze the machine. Nothing was responsive EXCERT my Magic Trackpad which moved the cursor but would not select anything. Thinking I had a ram problem, I took put the new and put in the old...same thing. Tried doing a reset of the PMU but it didn't work either. Now on restarts I even get the yellow spots on the Opening grey screen. Sometimes it will frizz there (cursor still moves) or goes through with the boot, only to freeze a few minuets later. (Cursor working and blue or yellow spots everywhere. ANY ideas???