Replacing DIMMs

[Stanka1]

I  I prepairing to replace DIMMs im my computer HP Compaq dc7900 Small Form Factor. What happens when I replace the DIMMs? The first photo is new DIMMs and the next photo is the existing DIMMs.

[BeemerBiker]

Use compressed air to blow any dust out before removing the memory chips,  With the system unplugged from the wall remove all memory chips and insert your first chip into the black socket #1 as described starting on Page 3-4 of the following document

http://h10032.www1.hp.com/ctg/Manual/c01549447.pdf

turn the system on and look for any error messages as described quote

If an incompatible memory module is detected the NUM LOCK will blink for a short period of
time during POST and an error message may or may not be displayed before the system hangs.

If the new stick of memory works then unplug  and add the remaining.  Channel A is the set of black sockets

[Stanka1]

What happens when I replace the DIMMs and turn on the computer?

[BeemerBiker]

Should work OK otherwise the following

If an incompatible memory module is detected the NUM LOCK will blink for a short period of
time during POST and an error message may or may not be displayed before the system hangs.

[Stanka1]

When I replace the DIMMs, it causes to freeze my computer during POST?

[Prométhée]

Hello
Give all possible details, otherwise you will just have an endless question / answer game
You show four hp memory modules.. ok?
you show two other modules of brands and can be of different characteristics?
You say you want to replace the modules, but only two then?
@BeemerBiker  told you to try just one..
then you just say
"When I replace the DIMMs, it causes to freeze my computer during POST?"
but you don't say the result of the tests he told you, do you?

your question
"What happens when I replace the DIMMs?"
The answer has been given, it seems to me.
If no problem, the computer should restart, normally..

So answer this correctly:
what happens if you remove all hp modules, and just restart with a new module?

What if it works fine with a new module, but then you add an original HP module?

good continuation

[Stanka1]

I will write a models of the DIMMs.

Slot #1: Hynix HYMP112U64CP8-S6

Slot #2 - #4: Micron MT8HTF12864AY-800E1

I don't have a four HP DIMMs. The DIMM sticks is not the same manufacter.