Hello everyone,

I have a PC (HP Compaq dc7900 Small Form Factor) which stopped working. The power light is on and green, the light on the motherboard is also on and green, Power Supply is running, i can tell that from the LIGHTS that are on and the spinning fan at the back of the power supply itself.When i plug in the power cable to the power supply the CUP Fan STARTS spinning and all the lights in the front panel goes on, but there is no display in the monitor, no any signal in the keyboard as well as on the optical mouse. I unplugged everything and STARTED putting back each device one by one, still to no avail. Tried changing CPU, no success.

One question, why is it that when i plug the Power cable to the power supply everything starts running without hitting the power button at the front panel?

I have searched for any similar issue of this PC on the net i found nothing, am i so unlucky to be the first one to experience this fault?
please. Once you have the computer running by attaching the power cord what happens when you try to shut it down from the power button? Have you tried your monitor on another computer? What if any software /hardware changes have you made that were coincident to this phenomenon occurring? Dows anything even for a brief instant appear on the monitor--even a flicker or flash? truenorthTruenorth thanks for your prompt response,

When i press the power button once nothing happens the CPU fan continues running and both the motherboard and the front panel light does not go off. But when I press and hold the power button for few seconds the CPU fan stops spinning and the front panel lights switch off, I changed monitor from a different PC still no success. The only signal i get on the monitor is from the monitor itself (DVI... NO Signal - VGA... NO Signal) this for sure is a monitor massage and not from the PC.

Any further help, welcomed.lino124, Your notation that you must hold the power button for longer than just a brief push is normal when trying to "shut down" a computer via that method. It is different that when using it at start up where pushing it for the briefest of time will (normally) start it. At this stage bringing another monitor TO the affected computer is NOT conclusive. What i would like you do do is take the original monitor to another computer. What i am trying to eliminate is that it is a monitor problem If the monitor works elsewhere then the problem could be your video card in the original computer. Are you sure that it was the "CPU" you changed? That is a bit drastic at this stage as it introduces other possible issues depending if it was done properly. You sure you don't mean the PSU the power supply unit?truenorthTruenorth, Yes i did swap the CPU as well even though it was bit drastic, that was just to eliminate the doubt of a faulty CPU, but i can reassure you that i returned it safely to its place. So here is what i did again, i got a working monitor tried it on the faulty PC still no success, i plugged in a PCIEX card switched on the PC still not solution, the DVD drive opens and closes smoothly. My question is: isn't there supposed to be at least one bip SOUND when a PC is powered on? there is no any kind of sound at. What is stopping the PC from TRANSMITTING any signal to the monitor? Did HP publish any Diagnostic Documentation for this Model?

Going to give you some web link in the hopes that it might assist you.
http://h20000.www2.hp.com/bizsupport/TechSupport/SoftwareIndex.jsp?lang=en&cc=us&prodNameId=3785038&prodTypeId=12454&prodSeriesId=3785403&swLang=13&taskId=135&swEnvOID=1093

http://bizsupport1.austin.hp.com/bizsupport/TechSupport/SoftwareDescription.jsp?lang=en&cc=us&prodTypeId=12454&prodSeriesId=3785403&swItem=vc-65111-1&prodNameId=3785038&swEnvOID=2096&swLang=13&mode=4&idx=0

http://h20000.www2.hp.com/bizsupport/TechSupport/SoftwareDescription.jsp?swItem=vc-65111-1&lang=en&cc=us&idx=0&mode=4&

http://drivers.windows9download.net/desktops/hp-compaq-dc7900-small-form-factor-pc-hp-insight-diagnostics-offline-edition.html

http://www.webstatschecker.com/stats/keyword/drivers_for_hp_compaq_dc5100_sff

truenorth
P.S. Just before i close here are some quotes from others on a different forum that were dealing with your problem. Don't know if they are applicable to your issue but including them in case they are.
"Ok I figured it out myself
It turned out to be the wireless pci card
After I pulled the card the pc no longer turns on when I turn on the power strip
Maybe it can be disabled by software I don't know I haven't looked into it that far
For now I am glad I was able to fix this mystery"

"Those of you with pc's starting up unexpectedly:

1. Check your power management settings in BIOS.
2. Check your power management settings in Windows.
3. Does your keyboard have a power management key that may have accidently been pushed?

Those would be the three most common solutions. We just had a thread the other day and it turned out a user's friend accidently pushed the power management key on the user's keyboard. Another user accidently changed Windows power management settings."