Per this site https://support.hp.com/nz-en/document/ish_1997210-1528385-16
=== The red light blinks three times, and then two, short white light blinks (3 long red, 2 short white) ===
This condition indicates a potential memory failure.
==== Test computer memory ====
==== Reseat the memory module ====
==== Replace the affected component ====
You may have incompatible RAM. Remove all the new RAM and try.