Black screen and 3 beeps

My iMac 27" showed the Kernel-Panic massage during some video work with iMovie. After the restart the screen stayed black and there were three beeps, a pause, and three beeps again. I looked it up at the apple-website and they said that it is faulty ram of some sort. I tried the usual smc and pram resetting as well as remove and reinstall the ram modules with no success. Is it definitely the ram i have to change or may it be something more serious? Any ideas?

Thanks Soenke