Greetings,
Welcome to the forum.
I am not a HP employee.
I can't locate your PC using Elite CD2. The forum needs a HP product number to check the age of the PC.
The GPU is working but the PC cannot POST or load the operating system. Can you get to the BIOS by usually tapping "F10" at system startup?
One can only guess at this point. Maybe the new memory? Did your PC work correctly before installing new memory?
Some component is causing this startup error.
Regards