ok, first of all, you learned your lesson, avoid asus

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2nd issue is that maybe its not the motherboard thats failing or theres something causing them to faill, first thing off the books i would check is the PSU, a cheap PSU is basicly an accident waiting to happen, if you plan on testing and suspect that the issue causing the problem is still out there, you should go for the cheapest decent board you can get, like asrock,
now the psu can be checked with a voltage/amp meter, all you need is to short the gray/black and the green, its the 3rd on one row with the 4th from the other side on 2nd row, you can find a diagram of the connector online, just short the power and ground to start up the psu (make sure you use a wire had has some isolation on it, you dont want to get curley hair while doing it, and remember to wear rubber sole shoes)
once the PSU is runnign, start mesuring voltages with the voltage meter, if you see that voltage vary or are significantly off (more then 0,3v) toss the PSU in the garbage, not worth using,