My HP ProBook Elite laptop is not turning on?

My HP ProBook Elite laptop is not turning on. The power light is constantly lit and the two lights on the edge are lit.

When I press and hold the power button, nothing happens, it remains on.

When I remove the battery and the power cable, all lights go off. When I put the battery back in (no power cable) the power light and two lights on the edge instantly light up.

The screen always remains black.

Normally I have found removing the power completely sorts out most issues. This time the power is behaving strangely. I don't think the laptop is attempting to start windows.

Is there any other reset I can do?