I have most motherboard which formerly used for cybercafe since it closed 3 year ago. When I using that, there no sign of power and it doesn't turn on. I think the motherboard was dead. How to repair them?
There's almost no way to know what's wrong, and even if you did, unless you know how to replace whatever component is damaged on it and/or fix damaged traces, it's just a MUCH easier proposition to buy a new one.
That mobo is a loss. Time to buy a new one or just not worry about it.
if the mb is out of warranty..some have three year or more. see if online there a debug guild or circute diagram online or from the vendor. you then need a volt meter and a scope. you have to look for missing voltages and signals on the mb. the first part of debug would be a post it card. it help see where in the post the mb fails. there are some places in post failure that you cant fix as a user. (if the mb north or southbrige fails.) you need some fine solider skills to redo those chips.
Defective capacitors are often obvious. Google is very friendly, and will be happy to show you images of them. Replacing capacitors on a motherboard is not particularly difficult, but it does take a steady hand.