Hello Mycroft mate as a general rule running a higher frequency RAM stick in a machine that runs that only supports the lower one the frequency will revert to the frequency of the new stick will be maxed to what frequency your machine will support. So I think whoever told you could run a higher frequency RAM stick in the machine should have known better and to get you to check out the supported RAM speed before you went out and got the new RAM.
If possible I would get the supplier to change it for 1333 (there really isn't much to be gained from 1600) and the extra RAM will still make a difference to your machine simply because the system has more to use and therefore less bottle knecking
- in other words the CPU can load more faster if it has more empty RAM available.
ie Tip a bucket of water through a 1 inch outlet funnel into another bucket and it fills quite nicely in say 5 minutes - now take a funnel with a 10 inch outlet and the second bucket fills in no time at all - the first bucket is the CPU and the second bucket the RAM the difference being there is more channels for the data to flow through even though it might be the slower speed RAM
You can see from this
Intel® Desktop Board DH55TC the board only supports 1333 max - you can install a faster RAM stick but why bother?
So for example the 1600 you have put in should only run at 1333 if the machine specs say max 1333. The other problem could be that the new RAM stick is bad.
To see about RAM this might give you some idea of what it is all about
https://en.wikipedia.org/wiki/DDR3_SDRAM
Just so you know I have a desktop that has 2400 RAM in it and fully clocked as opposed to the 1333 stock speed of the clockable board is in my mind a non goer - that machine runs faster because simply I have more RAM in it and not the speed of the RAM.
I think if you have 4GB in now give it another 4GB and you will be very surprised.
If you want more out of the machine check this out
Optimize Windows 7 but only when you have the problem sorted.