GA-N650SLI-DS4L can't install memory into slots 3 and 4

[Dark Mantis]

In that case I would think that there is no way to turn off Dual Channel mode for the meory and you would have to put in another matching pair of modules to get it to work.
Feel free to check the CPU socket pins if you want to but I think this explanation is far more likely.

[nga]

Thank you.

However, did you mean there is no way to turn on the dual channel mode? When I use the matching Hynix pair only in slot 1 and 3, the computer does not boot! I feel like both slots in the second channel (3 and 4) are faulty. But if it is the case, how can the whole system runs just fine when I use only slots 1 and 2.

[Dark Mantis]

Ok let's just check out the CPU socket to make sure there are no bent pins.
Very carefully remove the heatsink and fan. Probably a slight twisting motion is best to release the two as the thermal paste can act like a glue.
Once off remove the CPU taking extreme care both pysically and electrically(static) and place somewhere safe.
Make sure that the lighting is very good and even.
Now scrutinise the socket for any pins that are out of alignment, even slightly.
If in any doubt whatsoever take a couple of macro (close up) photos of the socket and post them on here for us to check.
Also look at the bottom of the CPU at the lands (little copper circles) and make sure that there is a mark in each somewhere near the centre.
If there are any missing marks or any of the pins are obviously bent then that is your problem.

[nga]

Ok, I will do that. As I need my computer until this Friday, I will look at the socket pins on Friday and upload images on here to ask for more help from you. Thank you very much for giving me instruction, I appreciate this a lot. See you on Friday then.

[Dark Mantis]

Make sure that you have some thermal paste to replace the old stuff on the heatsink/CPU joint.