Computer won’t post with 2 sticks of ram

[Silkymk]

I’ve upgraded the RAM in my pc about 2 years ago and it’s been running fine,

the pc has been powered off for a few months and the power supply has been changed for the exact same model.

ive also changed the CPU.

now the computer won’t boot with 2 sticks of RAM. (There’s only 2 RAM slots on the board)

any ideas? 

[Prométhée]

Hello
you do not specify everything!
Memory has been replaced, what exactly did you install?
The pc has not been used for a while, ok ..
But the power supply was replaced before after.
The processor also, at the same time as the power supply, before, after?
What has it been replaced by?
the computer no longer starts with two memory modules, it starts with only one, one or the other?

The product page tells us this:

•  HP Pavilion 550-152na Desktop PC Product Specifications
•  motherboard specifications, Odense

• Amount: 8 GB
• Speed: PC3-12800 MB/s
• Type: DDR3-1600

• Dual channel memory architecture
• Two 240-pin DDR3 DIMM sockets
• Supports the following:
  • PC3-12800 (DDR3-1600)
  • PC3-10600 (DDR3-1333)
• Supports 1 GB, 2 GB, 4 GB and 8 GB DIMMs
• Supports up to 4 GB on 32-bit systems

  note:

  32-bit systems cannot address a full 4.0 GB of memory.

• Supports up to 16 GB (unbuffered) on 64-bit computers

Intel Core i5-6400

• CPU speed: 2.7 GHz (max turbo boost - 3.3 GHz)

Processor upgrade information

• TDP: Up to 65 W
• Socket type: LGA 1151
• Motherboard supports the following processor upgrades:

  Processor	TDP	Integrated Graphics
  Intel Core i7-6700T (Skylake) 2.8 GHz Quad Core	35 W	Intel HD Graphics (GT2)
  Intel Core i7-6700 (Skylake) 3.4 GHz Quad Core	65 W	Intel HD Graphics (GT2)
  Intel Core i5-6400T (Skylake) 2.2 GHz Quad Core	35 W	Intel HD Graphics (GT2)
  Intel Core i5-6400 (Skylake) 2.7 GHz Quad Core	65 W	Intel HD Graphics (GT2)
  Intel Core i3-6100T (Skylake) 3.2 GHz Dual Core	35 W	Intel HD Graphics 530
  Intel Core i3-6100 (Skylake) 3.7 GHz Dual Core	65 W	Intel HD Graphics 530
  Intel Pentium G4400 (Skylake) 3.3 GHz Dual Core	65 W	Intel HD Graphics 510
  Intel Pentium G4400T (Skylake) 2.9 GHz Dual Core	35 W	Intel HD Graphics 510
  Intel Celeron G3900 (Skylake) 2.8 GHz Dual Core	65 W	Intel HD Graphics 510
  Intel Celeron G3900T (Skylake) 2.6 GHz Dual Core	35 W	Intel HD Graphics 510