It's hard to know for certain what the root cause is. When you turn on your car, it will spike the amp, without proper or faulty protection & soft start circuits, the amp is vulnerable. If the outputs mosfets recieved a signal or spike when they are not ready, they can blow out. Also, mishandling static sensitive Mosfets can cause the the device to become compromised. Static charges will perforate the internal leads and greatly shorten the life. Always leave devices in the sleeve or static free bag,and handle them as little as possible. There are other recommendations which I'm sure you can goolge or find useful tips on Perry Babin's links.We've all blown up a few amps or had duds on our benches. Sometimes the best thing to do is cut your losses and move on. The next time will be a better experience if you keep in mind the pit falls, take it one step at a time and asked questions until you have a good understanding of the steps you need to take.