... but when the cpu shuts down totally and wont power up, no sound beeping no led light , your psu is the problem./quotemsg]
Simplistic and inaccurate. No boot/no beep can be bad or overloaded PSU, bad motherboard, bad CPU (but unlikely), or a shorted component plugged into either the PSU or the motherboard. No motherboard power LED (actually indicates that you have standby power) usually means bad PSU but it could mean a problem with input power such as problem with wall outlet, AC power strip, or PSU power cord.
You can also have the standby LED on and the rest of the PSU dead.