I doubt it is the cpu. I would try to boot woth only one stick of RAM and then try the other. Make sure that you plugged all the power connector. The large one (20+4 pins or only one 24 pins) AND the small one appart of the main one. Unplug all hdd or dvd and try it out of the case on a non conductive surface.
I suspected the APU as I was getting a lit LED indicating a memory fault as well as the graphics issue. I tried both/single/no sticks in various configurations but still had errors.
It is now working fine after I removed and re-inserted the APU. However, I had to remove an re-attach the HSF in order to re-insert the APU so will likely need to invest in a good cooling solution as it's now likely less effective than it should be (getting as much as 62c at idle, fan at 5000rpm, which is insane).
Making do with underclocking and undervolting (which Llano APUs can apparently cope with quite well) for now.