Are you sure it's the motherboard?....

Remember, the motherboard can be a source of a lot of computer problems. With this in mind, a lot of support from companies will send you back your product after diagnostics saying the motherboard is bad. When you get someone saying that, check for yourself. Open the case and look inside, is there a lot of dust?... If that's the case, then you'll want to clean it out, like you should every 2-3 months depending on your environment. Shop computers should clean their computers every month. What was the problem with the computer? Not starting? No video?... Look for the true source of the problem before you check anything on the motherboard. If there's no video and you have onboard video, there is no fix for it, besides getting right drivers. You could install a video card into an available slot but there still could be other errors on the board. If your computer dosn't start up you should always assume the power supply is the source of the problem first. Look at it, does the fan spin up? Does the motherboard have a green light?... To test if it's the power supply you could get a paper clip and shove it from the green wire to the black wire next to it and see if the fan spins up... but for amateurs I don't recommend this.

Just all in all, make sure it really is the motherboard before you go buying something you don't need. You may have a power supply problem that'll cost you $20. Or you could have a CPU problem and save yourself $100 by not replacing the board. Always be sure of yourself before you make that final spending decision.