RAM caused issues.

Okay, so. My girlfriend had an older PC and a newer one but basically the same looking things, except the other one was just a tad bit faster with the processor. So i decided i could boost it up by taking out the RAM in the older one (by the way, both computers worked fine beforehand) and putting it in the newer one (since the newer one didn't have as much RAM, which required me to take out the chip it had in there). So i swapped RAM's just to see if it'd work and when i boot up the PC it makes this beeping noise and nothing comes through to the monitor, so i was like hm. So i took everything back out and put everything the way it was in both PC's and it still did it..but in the other PC as well. So i have both of them beeping and nothing coming through. All i was doing was trying to swap RAM and now they're both going crazy even though they're put together the exact same way as they were before. I tried EVERYTHING and it's still being nuts. I'm stumped.