Hi, the problem I had from before (laptop not booting first time) is persisting and worsening. It now takes up to 20 attempts. Diagnostics are completely clear.
Disconnect all external devices, and the AC adapter. Disconnect or remove the battery. Hold the power button for 30 sec.
Remove the base cover, memory modules and hard drive. Reinstall these components.
Leave the AC adapter plugged into the wall - but not the system. The LED on the adapter or DC plug should be ON. If it's not, replace it with a new one.
With a working adapter, connect the system and power up. If it'll power up reliably without but not with the battery installed, the battery is bad; replace it.
If it won't power up reliably thereafter, you likely have system board going bad.