NEw ram stick, no boot. Old ram, does boot.

[Lagoobrius]

When I put my new stick in with my old one, it worked a bit, then it wouldn't boot starting yesterday. Tried removing new stick, it does boot. Whenever the new stick is in, it won't power on my keyboard, monitor, or anything. Only says its on and fans spin, but no visuals.

[Prométhée]

hi

if the computer cannot restart with the new module alone, do not insist
replace it!
be careful, because sometimes it will absolutely be necessary to change for two modules, old and new are not always compatible with each other!

8 GB DDR4-2666 SDRAM (1 x 8 GB)

but see this

Memory upgrade information

• Dual channel (1 DIMM per channel) memory architecture
• Two DDR4 UDIMM (288-pin) sockets
• Supports PC4-25600 (DDR4-3200)
• Supports 4 GB, 8 GB, and 16 GB DDR4 UDIMMs
• 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 32 GB (unbuffered) on 64-bit computers

https://support.hp.com/us-en/product/hp-pavilion-desktop-pc-tp01-0000a/37874144/model/31588445

[Lagoobrius]

So, do I get a second duplicate ram stick or a new one?

[Prométhée]

I don't quite understand your question, but:
either you buy a module, as close as possible, identical to the one in place, and if it works, so much the better!
either you buy a new module, which should be compatible, check which one is in place, or buy a similar one
Try the new one by yourself, in order to check whether it is compatible with the motherboard..
if no problem, try with the old one
either it works or you will have to buy exactly the same as the new one..
you understand, sorry, it may not be clear to you?

try this

CPU-Z | Softwares | CPUID

and scan

Welcome to Crucial USA

be careful when handling the modules, and the inside of the computer (especially static electricity)

Upgrading and Servicing Guide

IMPORTANT: Follow these part replacement instructions:

CAUTION:
Never open the cover while the power cord is attached. You
may damage your computer or be injured by the spinning fan
blades.

 Avoid touching sharp edges inside the computer.
IMPORTANT:
This product contains components that are easily damaged by electrostatic
discharge (ESD). To reduce the chance of ESD damage, work over an
uncarpeted floor, use a static dissipative work surface (like a conductive
foam pad), and wear an ESD wrist strap that is connected to a grounded
surface, like the metal frame of the computer.

A hard drive is extremely sensitive to shock and impact. Do not bang or drop
it. Do not touch the circuit board. Static electricity can damage the drive