I bought some used DDR2 DIMMs to match a pair what I had already. I inserted them into my good PC and it would not boot - no display, not even a beep error code.
So I removed the suspect DIMMs, and still my PC does nothing. Only after replacing the original DIMMs with a third pair did the PC boot.
Next I put the suspect DIMMs in a spare computer, and it gave beep code for
memory failure (has a different mainboard to the other PC). Also tried the original DIMMs that were good, and found they also give bad beeps. So it appears that I got some bad memory which furthermore damaged the original RAM in the nearby slots. I contacted the seller who swears on a Judeo-Christian storybook that they were A-OK when he posted them. They were wrapped in an anti-static bag.
I have been building and upgrading PCs for over 15 years, and have never zapped any modules. And both PCs were set at standard frequency and voltages.