Mac not powering up when I hit power button?

imac 17 inch 1 83 GHtz Core 2 Duo

Ok came home one day my mac was off I normally leave it in sleep mode. Tried to turn it on just wouldn't come on. Asked my daughter if she was on it she replied yes and I was doing something and it just shut off. I asked what she was doing,she replied making a cartoon and all of a sudden it shut off. This was a couple days when I asked this. Went online to apple checked all there trouble shooting information and did all that they had. It all pointed to the power supply. Took it apart replaced the power supply and reinstalled it back,plugged it back in and I still have nothing,no lights,sounds nothing at all. It hasn't been dropped. Have a friend who is a computer diagnostic person, called him when he had time and we did all the same things I did he suggested that the power supply was the problem he gave me your web site on how to disassemple and reassemble my imac.

I haven't gotten a new cord. Now I'm confused any suggestions would be great. Followed the directions online foward and backwards don't think I missed a step I don't have any extra parts (joke) Thanks for the help in advance.

Okay have an extra electrical cord off another screen, checked to make sure it would plug in and correct style plug. Plugged it in and still have nothing, don't get it. Oh when I used the other cord yesterday plugged in to outlet downstairs didn't work, plugged into apc battery backup upstairs got a spark like a power surge when I plugged it in could I have just wasted the new power supply? I know power surges not good for any computer. Again thanks.