PC NOT SWITCHING ON

I am having a branded pc.I am facing a peculier problem for the last one month.When ever I try to switch on my PC, it never switches on always.
I have to keep on trying randomly,but it switches on on its will and wish.Once it switches on it doesnt pose any problem.Even technician could not find any fault in it.All the parts are fine.Even there is no problem with power and power supply.