Problems with buying another stick of ram for my pc

Solution
It is always a gamble to mix memory modules to increase your total ram unless the DIMMs are purchased as a matched set. The risk of failure increases when the DIMM modules are NOT even rated the same speed.
My suggestion is to return the single 2400 module and get a matched set of 2133 DIMMS. Probably save a lot of time and trouble in the long run.
As an example: I had 3 matched Crucial DIMMS that worked well together; replaced the mother board and now had 4 slots so I called Crucial and their Tech Support worked with me to find a module identical to the 3 I had. Installed it into the new MSI board, it was recognized, but nothing I could do or did ever made that board run in dual channel mode - until I bought a matched set of 4...
It is always a gamble to mix memory modules to increase your total ram unless the DIMMs are purchased as a matched set. The risk of failure increases when the DIMM modules are NOT even rated the same speed.
My suggestion is to return the single 2400 module and get a matched set of 2133 DIMMS. Probably save a lot of time and trouble in the long run.
As an example: I had 3 matched Crucial DIMMS that worked well together; replaced the mother board and now had 4 slots so I called Crucial and their Tech Support worked with me to find a module identical to the 3 I had. Installed it into the new MSI board, it was recognized, but nothing I could do or did ever made that board run in dual channel mode - until I bought a matched set of 4 Corsair modules. RAM can be really strange.
 
Solution