loose power plug at the back of the psu.wiggle the cord with the computer running and see if the computer shuts down.if the plug is tight in the back of the psu then likely you will need a power cord.if the plug is loose you can try a few wraps of electrical tape around the outside of the plug for a tighter fit or just replace it with a new cord.
Unplug the PSU power cable.
Press and hold the PC power-on button at the front for 10 seconds.
Reconnect the power cable.
Press power-on button & it should now come to life.
If still no joy, replace the fuse in the PSU power cable plug.