Hi
Depending on the age of the PC and the BIOS vendor...
https://support.hp.com/us-en/document/bph07107
EG: -- LED blinks 4 times --- Graphics
Graphics controller failure.
Test the Main-Board with the minimum hardware & re-seat all connections and graphics cards.
If the issue persists, send out Main-Board and if applicable graphics card for Mobile Workstations.