Hp pavilion 752n wont turn on.

Try holding the power button in for 5 seconds at least. Then wait 30 seconds and briefly press the power button as normal.

check the fan and see if it is busted or any of the cables

In my case it turned out to be a weak power supply. It would work sometimes and not others. If stone cold, it would not boot. If I unplugged 1 thing, like the hard drive or the CD Roms, it would boot. Tested the old power suppy and it seemed to pass. But once I connected a new power supply, the computer has worked fine ever since.

I suggest to open your computer and unplug your power supply and look for the color green and black cord which plugged from your motherboard. Then find a piece of wire and short the color green and black wire to test if your power supply is working and plug to your power socket. And check your electronic parts (capacitor) near at your processor, it might your capacitor blown out.

verify if at rear is a button with 1 and 0 position
that must be on 1

posible the PSU has failed or have a short somewhere inside case/MB/hardware

taking out the battery resets the settings on the bios for the motherboard.

worked for me on the few computers that wont turn on.

If it starts up, you may need to enter dates etc onto the bios.

Check your BIOS battery make sure it is working correctly and that it is not out. You can use a battery tester to see.

Did the switch on the power supply get bumped?
There will be a toggle switch. one side has O and other side has - . It needs to be on the - to turn on.