- Mixed RAM modules are not guaranteed compatibility. RAM is ONLY guaranteed in the form sold (from the exact same pack) and it is quite common for mixed modules to cause a no boot, or instability issue.
- Running 3 modules on a dual channel board, unless the additional memory is required by your normal usage of the PC, can slow down RAM performance as you are accessing 3 modules from only 2 channels. Usually for gaming 16GB is more than enough for example.
- On top of this the 2 modules are different speeds, which can create a little more risk of problems. That and the 3200 RAM will likely downclock to match your 2400 RAM.
- You'll want to make sure you reset CMOS when you install the new RAM module, and sometimes it can take a little time before boot as the system is configuring the new RAM. You also want to install them as per the motherboard manual .
But again, ultimately, mixed RAM modules have no guarantee of working together at all anyway. If you want to test the individual RAM module, you can remove the previous pair and simply install the 16GB and see if it boots normally.