I am a Pc technician.But new in Hp product. The problem am facing right now in my hp dc5100 sff desktop are as follows: I have a System that is not receiving power. After verifying that the problem is not from power cable and socket switches, I swapped the psu unit with another compatible working PSU(power supply unit) then the board now receive power. but try to power it on, I notice a 9bit sound with a red light displaying during the beep. What do I do from here? pls get back to me now. thanks favour.

Hi, Please try changing the slots of the ram(memory) or if possible try changing the ram. If you have more than one ram installed then try removing them one by one. Also please check the wire that is coming from the power button and going into the motherboard pins(pins where the wire coming from the power button gets fitted). If this doesn't work then the problem is with the motherboard. Please check the large capacitors around the motherboard are fine or they have blown out.
Hope it Helps. Regards Anand Sachan