Woah, slow down there. Nothing happend for no reason, but sometimes the reasons are well hidden.
A virus will not 'kill' motherboard or processor, but can destroy data stored on the hard disk. This can (in extreme cases) prevent the PC from starting. However, unless the power supply is completely dead, the PC will nearly always do something even if it is only a line of text or a flashing led.
Beginning from when you push the power switch, please say EXACTLY what happens - text on the screen, beeps, led lights flashing etc. How far does it get (if at all), does the screenlight up or change colour, all this is important.
What kind of technician was it ?
Tell us what you know about the system, how old it is, what version of windows etc.