+1^ Corwin is right on the money. What are your system specs? Also, can you list games that won't work? This will help us give more accurate answer to help you.
Have you installed all the latest drivers? Also, would be a good idea to update the bios too, if you haven't already. But given you have a B350, you must have a pretty recent one as it needs it to run the 2400g. Are you using Vega GPU or an external graphics card?
Ryzen likes fast ram, yours is a bit slow. You should still be able to play though just at low settings and low FPS.
What game are you trying to play? Are you considering getting a dedicated GPU?
I do agree ryzen likes faster ram, but in the case of 2400mhz v 3200mhz, the difference in gaming FPS is typically 5-10%. Sometimes more. But that often translates to just a few FPS, so that's not the problem here. It won't impact the overall performance of the GPU too much. If the games don't run at all, there is something else at play.