When second RAM is installed, no signal monitor and cpu fan not rotating problem

May 23, 2018
Hey guys, I got old PC from my dad, with mobo ga-945gzm-s2. I bought new graphic GeForce GTX650, cause I want to "upgrade" that senior comp a little for my brother. Bought some better PSU 400w for it, and bought two 2G RAMs that are the same. After I succesfully installed them both, PC was working well. But then I bought some newer mobo, which was not compatible at all, so I decided to get it all back to old mb. When I installed first RAM it was ok, all worked, but second was problem. I tried every slot (2, hehe) RAM is working single in first and in second slot ok,and when I turn the PC on, the CPU fan is rotating. But when I install second RAM, PC will turn on, but CPU fan is rotating for a few seconds, then stops, and then it's working just when I turn off the PSU button, and no monitor signal as well. Oh, and second RAM is working in single channel as well. I tried the same with old 1G RAMs, but it's the same problem, no monitor signal and CPU fan is not working. I searched lot of threads, but I can't find anything with CPU fan not working when dual channel RAM is installed. Everything is installed correctly (I am sure...), I tried update a Bios, but still the same and I have no clue why it worked before, and now it's not. When I turn the PC on, it will show something like "PC is running single channel", It's possible that some settings in Bios are bad? like enable a dual channel RAM or... I found thath it's not necessary, that PC will detect a dual channel RAM automatically.

Sorry for my english, and thanks for all answers, I hope that we will find the problem. :) And no, I will not throw this old PC from the window. Have a nice day!
There's no single or dual channel RAM how they work together is up to CPU and BIOS. For dual channel you have to have 2 working sticks, only one at a time would run in single channel. Make sure youreset CMOS/BIOS between any changes of RAM.