Zacal bych cistou reinstalaci Windows.
Pak bych vymenil power button board, to stoji par stovek.
https://www.ebay.com/itm/New-for-hp-ProBook-4740s-Power-Button-Board-w-Cable-684613-001-/174057998990
Do vymeny motherboardu bych se uz nepoustel, to uz je za hodne tvych tisicikorun.