Windows 7 - Newly assembled screen problem

Hello SF
I've just assembled a pc using different parts from old computers. For some reason my pc will turn on, but my screen just stays black. I've tried several graphic cards, nothing. How do I determine if its really the motherboard failing without a screen ?

First (obviously) you test the monitor and cable on another system.

No video can be caused by a bad video card, bad RAM, incorrectly installed CPU, incorrect BIOS setting, power supply, and finally MB.

You want to do some diagnostic tests to try and zero in on which component is the problem one. As you do the following diagnostic tests you should take the time to reseat the components carefully and double check all of your electrical connections.

The Test:
Basic diagnostic procedure is to uninstall the entire build and start over. Some people do this out of the case by placing the motherboard on an anti-static surface. This eliminates the possibility that there is a short circuit between the motherboard and the case through the connection posts (stand-offs). A standoff in the wrong location or a sloppy job will cause a short.

The Test (power off, power cord unplugged):

• Disconnect everything externally connected except the mouse and keyboard (printers, USB devices, etc). If you are not using a wired mouse and keyboard see if you can borrow one. The wireless device is just another component you have to deal with.
• Disconnect the power and data cables from all the drives inside the computer (Hard drives, DVD/CD drives, etc).
• Remove all the cards installed in the expansion slots (PCI/PCI-e) including the video card. (Be careful handling them and place them on a non conductive surface while testing).
• Remove all the RAM sticks (same rules as above).

Now connect the power cord and turn the PC on.

• The motherboard should start beeping. You should get a beep code that tells you there is no memory. This is good, it means the processor is functioning and the motherboard is good so far.
• Now add one stick of memory in Slot A1 and power on. More beeping: "no video card" beep code. This is good.
• Then add the video card and connect it to the monitor. You should get no beeping and you should see the BIOS start screens, ending with the message that there is no boot device.
• If you get no video then switch the one memory stick installed for another one and test.
• If you do get video then start adding components back, one at a time, until the system fails to boot. The last component you added is then the problem component.

First problem occured when I disconnected everything the MB just keep silent... No beebs, it could just be me, I just replaced the CPU and putted on a layer of thermal paste, maybe I didn't do the correctly?

Also check to be sure the CPU you are using is compatible with the motherboard, or if the motherboard's BIOS needs to be updated in order to accept the CPU.

Most newer (post 2000) motherboards have a small piezo speaker soldered to the board to play the BIOS beeps, but older boards and some odd ones still require an external speaker be attached by wires to the speaker header on the MB.