I would contact HP Support (Link) if you have an extended warranty.
A green LED on the PSU usually means the power supply is probably okay. You can't chuck this component off the failure list.
There is no way to get to the bad component without troubleshooting the system by stripping down to bare essentials and replacing components. Many different component failures can cause this symptom. You could even have something simple like a dislodged PSU connection to the MB.
It is very difficult to troubleshoot this type of failure in a forum. Someone has to look at the system and review all symptoms before developing a plan to solve this problem.
A local PC tech is your best bet if your PC is out of warranty.