I added a stick of 4 GB of ram in my HP 15 it is not recognized.

[tomcon94]

I installed a second  stick of ram in my HP laptop, DDR3 PC312800 it did not recognize it. I placed it into the first slot it did restart but it did not add the old ram in the second slot. So I know it is the correct ram for the computer. I need to know how can I get the laptop to recognize it?

[Paul_Tikkanen]

Hi:

Does the original memory work in both slots?

If so then you know the slot isn't bad.

Your notebook uses DDR3L-12800 (1.35V) memory, not DDR3-12800 (1.5V) memory.

Installing the wrong voltage memory would be the most likely cause of your current dilemma.

[Maké]

Hi!, @Tomcon94 :

Your notebook, is ... https://support.hp.com/us-en/product/HP-15-ac100-Notebook-PC-series/8499326/model/10193201?jumpid=re...

The specification are ... https://support.hp.com/us-en/document/c04936088?jumpid=reg_r1002_usen_c-001_title_r0003

Have, the Maintenance Manual (generic) ... http://h10032.www1.hp.com/ctg/Manual/c04653884 

Have, memory ... (página 46)

8-GB - 1600MHz, PC3L-12800, DDR3 small outline dual in-line memory module (SODIMM) - 693374-005
4-GB - 1600MHz, PC3L-12800, DDR3 small outline dual in-line memory module (SODIMM) - 691740-005
2-GB - 1600MHz, PC3L-12800, DDR3 small outline dual in-line memory module (SODIMM) - 691739-005

"L" = Low Voltage = 1.35VDC

You can install 16Gb.(2x8Gb.) maximum capacity or too, 12Gb.(1x4Gb.+1x8Gb.) of recognized brand, as ... ADATA, Samsung, SKhynix, Crucial (by Micron), Corsair, Kingston, etc ...

For purchase ...

https://parts.hp.com/hpparts/Part_Resellers.aspx?cc=ES&lang=ES&geo_code=LA

https://parts.hp.com/hpparts/Default.aspx?mscssid=

Too, with Origonal (OEM) HP Part Number, from ... eBay, Amazon, etc ...