Power surge and is not booting up

Hi I have am Apple iMac 2009 27" and I had a power surge the other day but my surge protector failed and now my imac won't boot up. If I push the power button it start but sound like it only runs the cd drive then stop it and the hard drive sounds like it starts but no screen comes up no boot up noise nothing. My computer guys said it is probably the power unit inside but I want to see if anyone else has any possible theory's as to wat it could be

Many thanks chuckey