cant boot pc with new ram

Hello there, last week I gave a friend my old gaming pc. Since it only has 6GB ram, his parents bought him some new ram, he put them in. And the pc will not boot up. We have taken out the cmos battery and put it back in, and we have put in the old ram again. When I removed 2 out of the 3 ram...

So recently i started playing a game called ”Rust” and noticed that 8 GB ram isn't going to be enough to have stutter free gameplay. So i searched online that if you mix ram to try and use the same model of ram and brans and everything. I did just that and when i placed the ram in for first time...