PC turns on but won't boot up. Plz help!

[voldo3339]

I was playing a game on my pc and when i was done i turned the pc off.
When i tried to turn it on later, the fans (both cpu and case fan) were running at extreme speed. I couldent turn the pc off so i had to pull the plug.
I removed all cables, blew out the dust, turned off PSU and i plugged it back in, but it still did the same thing. I replaced the PSU and CPU. Also i have onboard and offboard graphics card, but the screen stays blank on both. I don't know if its the mobo, coz all the other parts are fine. Now about a week ago i noticed a change, when i turned on the computer the fans turned on and quickly stopped, with the same symptoms as before. Now when i turn it on, one of the two things happen, either the fans run at superspeed, or they run for about 2 seconds and then turn off. I tried 5 different cpu fans and the same thing happens. So i know the cpu, graphics, hdd, psu, ram are all fine.

I think its the mobo but im not sure. Does anyone know?

Also i tried removing the battery to reset CMOS, no results.

 

[schm1tty]

There is nothing wrong with the fan going fast at startup for a few seconds.

The issue is that the computer is not POSTing. POST stands for Power On Self Test and the computer runs that test every time that the computer is turned on. Now if a component is damaged or has failed, it can prevent the computer from completing its POST and it will just sit there with a blank screen. Right now you just need to keep isolating components.

Was there any storms or any power sags when the computer was plugged in?
Have you removed all devices from the motherboard(cd drive, hdd, pci nic, pci modem, audio card, etc.) to see if you can even get into the bios? If you remove every component from the motherboard and it will not even go to bios then it is most likely the motherboard.

Also, don't forget to test the psu. The psu sends a PG(power good) signal to the motherboard and if the signal is too high the computer will not complete POST so that the components are not damaged by the psu.

Now go test!
and good luck