My PC does not turn on when power button is pressed

Take a look at the keyboard caps lock key and listen for beep codes. 95% of the time, it is bad RAM or corrupted CMOS settings (SureStart machines only) due to how stringent HP is at POST about RAM quality on the Pro and Elite series. The HP Z series is far less forgiving, but these non-Z machines at least give you some room for error.

What is the pattern? The procedure for accessing the RAM and CMOS batteries is in the HP SM. Refer to this for POST codes.

Look at the pattern on the caps lock key, write it down and report back:

HP isn't so strict about it with Commercial BIOSes you can't run 3rd party RAM like Corsair or Crucial (retail Micron) - it just acts as a filter for the abysmally bad garbage you find on sites like eBay directly from China. Use good RAM and you will be fine.