The DH55TC manual
specifies two independent memory channels with interleaved mode support
with two DIMM sockets per each.
It further states :
- Support for non-ECC, unbuffered, single-sided or double-sided DIMMs with x8 organization
- 16 GB maximum total system memory (with 2 Gb memory technology)
- Minimum total system memory: 1 GB using 1 Gb x8 module
- Serial Presence Detect
- DDR3 1333 MHz and DDR3 1066 MHz SDRAM DIMMs
Better verify that your memory sticks obey the above criteria.
There is just one gray point in the above, which is that with the
mentioned "2 Gb memory technology" and 4 DIMMs,
the maximum RAM is no more that 8 GB, while the stated maximum is 16 GB.
The two numbers conflict with each other.
As there is a small doubt as to whether your motherboard can accept
4 GB sticks, I would counsel to only buy such sticks only if you can ask for
a refund if they don't work.
When in doubt, and to be absolutely sure,
I would suggest to download and run the
Crucial System Scanner
and see what it says about memory upgrades and possible configurations.
In my experience this tool is absolutely trustworthy.
As another advice, position the two larger sticks in different channels
and on the same DIMM (best both on DIMM 0).
The smaller stick can be positioned anywhere else, but be prepared if the
motherboard will reject a non-symmetrical configuration
(which the manual says nothing about).