Please HELPPPP

My problem is, I’m receiving a no video input error on the LCD after my daughter turned the power off, I checked all the connections and it was still the same,
The motherboard is an ASROC K8S8X with a 64 bit AMD chip, I thought it was the motherboard so I fitted a new motherboard and graphics cards and it's still the same, I’m thinking its the chip, There are no beeping sounds when you remove the graphics card or MeM, I took it to the local computer shop, He discounted the monitor and said everything looks OK, he couldn’t help.
I’m going crazy!,
Please could any one shed any light on my dilemma it would be greatly appreciated

Is the PC booting up? Or is it even powered? You should hear the fans and drives kicking in. If not, it could be the power supply or a loose cable from the power supply. It doesn't sound right for you to not get beeps if the memory is taken out, which makes me wonder if you have power.
If it is booting, try another video cable, and check the connections to ensure that all the pins are in place before spending any cash on new boards.