The new stick might be bad. You're putting it into a different slot so the bad part will end up somewhere else in the memory map so it might not trigger whatever breaks your video. If you swap it back and the video dies again then I'd get that memory stick swapped out.

You should run a memory tester like memtest on your PC. Download the zipped ISO and burn it as a CD image to a CD then boot off it. Just leave it running overnight.