To find out whether a motherboard is bad, Computer Hope suggests using diagnostic tools, such as Hot CPU Tester, that check for failures within a system. If a computer does not start at all, listen for a series of beeps when the power is turned on. The motherboard's manual normally describes each beep pattern and the hardware it is diagnosing as failed.
Chron Small Business recommends eliminating all possible options before removing the motherboard. Many other components could be faulty on the computer. Some viruses and malware can make a computer behave as if the motherboard is malfunctioning. Radioshack suggests checking all software before going inside the computer to examine the hardware. If software is functioning correctly, try to connect the computer with only the power supply and video cable connected. If the computer boots, try connecting other components one at a time until the computer fails in order to find the faulty hardware.
Chron also notes that if the motherboard does have to be replaced, it is important to find the same model so that all connections match. If the replacement motherboard is different, physical connections may be different as well, and more hardware may have to be replaced to match the new motherboard.