XPS 720... power issues

I have a xps 720 and it has just quit on me. The computer doesn't dignify me with a sound or a flash of light. I roamed around the house trying the computer on different sockets with and without the surge protector.... still nothing. I thought it might be the turn on button but it seems to  be functioning. I also tried turning the computer on by pressing the switch on the motherboard and nothing happened. I unplugged everything from the power supply and left the connections to the motherboard hoping the small yellow light on the motherboard would turn on... nothing. As of this moment I have my computer in parts and i have come up with three guesses to what is wrong. 

First.. it could be the power cord itself. I did have the cord harshly tucked in behind my desk. I have messed with it quite a bit with nothing happening. There is no damage when I look at it. 

Second... The power supply - nothing is working... no fans, sounds, or lights. 

Third... The motherboard.. I don't know a lick about the motherboard, but I have heard people talk of problems with it. 

I just need some feedback on what may work and how I can troubleshoot this problem. I don't want to scrap it... I have all the family videos and photos stored on the machine and would like them back.