My RAMs aren't working anymore !!

So my monitor keeps shutting off every time I play a game, and me and my brother suspected that the RAMs aren't plugged in good or something. So I tried to plug them in better, but still the issue's still there.

Keep in mind, I am not a professional, I do not know a lot about PCs, I know nearly nothing. Yes, I know it's weird, but my brother usually does everything.

Then, I did a search and figured out that the slots 2 and 4 work the best (I had them at 2 and 3, beside each other), so I plugged the RAMs there. But when I turned on the PC, one RAM was working only. I tried switching them, trying one RAM for both slots to see if it's a slot issues which turned out to be not because both RAMs work fine on both slots but not when I try to put them both.

I eventually gave up and put them back how they were—slots 2 and 3—and when I turned on the PC, none were working!

Please, I need help I don't know what to do!