Alright so after trying things, I have some bad news.
Once I put his second RAM stick to another slot that it could run dual channel, PC became unstable. Before windows started crashing, I managed to open up minecraft, but the frame rate was identical to the old one, so RIP. After that, I put the RAM stick to the previous slot (it's the first and second, I had put the second to the third position) Windows worked normally, didn't show any crashes. I could have done the first RAM stick to the fourth position, but I didn't want to corrupt any data so I left it be.
So, that is now out of the table O; I am officially out of ideas