Okay so basically, I've been running with two sticks, 4gb and 2gb DDR3 1600 MHz 12800 UDIMM in dual channel with zero issues. I decided to upgrade and add another 4gb. The upgrade is also DDR3 1600 MHz 12800 UDIMM. I installed the RAM for dual channel, placing the new stick in the slot the 2gb stick was in and moved it over (the first slot closest to the CPU is sadly blown out). I know that the other three slots work, as I have tested it with the RAM I have been using. Cleared the CMOS by removing the battery for 10 minutes (I know the reset worked because I had to switch back to AHCI from RAID, for compatibility with Win7) and tried to start everything back up. One of two things happen: either the motherboard returns a POST error (obviously memory related) or the system boots up, Windows 7 recognizes the additional 4gb but says it's unusable. Third party programs such as CPUID - CPUZ do not recognize the RAM as being present. Thinking it might just be a defective stick, I had the supplier send me a replacement, but the replacement does the same thing. The RAM should be compatible with the motherboard, but maybe there's something I'm missing? Any help would be greatly appreciated.
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I see from the post that you are having issues with upgrading RAM on your HP Pavilion Desktop PC. Don't worry as I have a few steps which should help you to resolve this issue.
Kudos to you for trying out the steps before reaching out to us.
After reviewing your post, this definitely looks to be a hardware issue, Before you could contact our HP phone support, I would suggest you try these steps here:
Let's start off by performing a Hard reset on the PC with all the cables disconnected.
Next thing, I would suggest here is to remove all the RAM sticks and then insert one RAM and check if it works on this slot. Similarly, try the same RAM on the other 2 slots, this will let us know which slot is causing this issue. On the other hand, you could as well try the other 2 RAMs one by one and check for the RAM.
Depending on the results, I would suggest you contact our HP phone support for available service related options. If your product is out of warranty, please choose paid options to get the tech support number.
Please use the following link to create yourself a case number, then call and it may help speed up the call process: