MotherBoard POST problem

I made a new PC with brand new Gigabyt GA-P35-DQ6 mother board with intel core2duo 2.13CPU and 2*1GB of RAM..AND GFORCE 7300GS GPU… it boots fine for first time when i start it…But after shutting down again i tried to turn it on but no POST no display……..again i need to unplug AC walloutlet…….again i plug it then it works …..or turning OFF PSU and again turning PSU ON then again Motherboard works fine ….this happens continiously.but the board is working fine with windows and everything untill i shut it down..no problem with restarting …..problem is only after shutting down.again turning on….i checked changing MEMORY,. PSU, GPU,no improvements…it sounds tik-tik-tik and HDD LED is up as per sound