The ram is not matched to the speed of the other chips and The other chips is not supported. While running with the original chips.
When buying new make sure to know the max speed the motherboard supports. And that you buy all the same type. by the same manufacturer.
Not all games have looked over their code for holes loops etc that will cause buffer overloads. because it doesn't unload a texture that is no longer used etc.
also do a virus scan, as many popular exploits now use some sort of buffer overflow script in cunjunction with several other tactics. It's old and known, but if hidden it's effective. I have had similar issues, when a remote computer tries to access protected files. The os and anti-v is instructed to shut down or restart, before they are able to try getting through.
Check your event logs, It may not be ram but a process or hijack attempt. either way you'll get a better idea of whee the problem is by looking this over real good.
What is the size of your virtual ram?