Had a similar problem. Asked the manufacturers and got this reply :
" This may be a problem related to a build-up in the Power Supply. With the machine powered off, remove the mains lead and then press and hold the power switch for about 15 seconds. Also remove any peripherals from the PC (printers, scanners, cameras etc) leaving only monitor, mouse and keyboard connected. Then re-insert the mains lead and try to power on again.
Also if the machine is on a surge protector please remove this."
Have done this but am still getting the problem from time to time