Theres no power when I press the power button

@sihlezwane there are instructions that are specifically for your system

Press and hold the power button for less than 4 seconds. If
the hard drive LED turns green, then:
1. Check that the voltage selector, located on the rear of the power supply on some models, is set to the appropriate voltage. Proper voltage setting depends on your region.
2. Replace the system board.
OR
Press and hold the power button for less than 4 seconds. If the hard drive LED does not turn on green then:
1. Check that the unit is plugged into a working AC outlet.
2. Open computer and check that the power button board cable is properly connected to the system board.
3. Check that power supply cables are properly connected to the system board.
4. Check to see if the 5V_aux light on the system board is turned on. If it is turned on, then replace the power button board.
5. If the 5V_aux light on the system board is off, then replace the power supply.
6. Replace the system board.

Check all of those things out and use the HP Compaq 8200 Elite Maintenance & Service Guide to work on your computer.