If they detect some kind of overload [current] it shuts the supply down. Sometimes it is only the inrush curent to drives/charging capacitiors the cause the shutdown. Have you added any hardware recently???.

Try disconnecting all of your drives [both signal and power cables] to see if the supply stays on. Then troubleshoot. Many other things can cause an overload, fried CPU, bad memory stick [if you have two, try one at a time. And, of course, the power supply itself can fail and shutdown erroneously.

AMD CPU's run hot as hades, so when you are in the computer be sure to first clean out all of the fans, dust balls, heat sinks et al.