Powerbook G4 1.67 Al 15" RAM issues

I recently installed two 1.0 GB of RAM. At first, my Powerbook was working fine, then three weeks after, I started having problems. The computer would freeze and I would get the Error screen. Now, it starts up and boots but no video. I ran the S-video port and DVI port to see if it's the screen and it does the same thing. I also replaced my PRAM battery and have tried the PRAM reset and still nothing. I only know now that it could be the RAM slots or logic board.

How would I determine which is it and fix it?