No power chime/no power/no fan/no noise when button press

When I try and turn on my mid 2010 iMac 21.5 inch, nothing happens. When I plug it in, the first diagnostic green LED turns on, and when you press the power button it immediately turns off and nothing happens. Literally nothing. Nothing at all. No chime, no other lights, no fan spin, no hard drive spin, nothing. I have ordered a completely new replacement board and put everything back together. The same problem happens. Could this be the power supply? I ordered one off of eBay and it should arrive on friday, the 10th. What else could this be as I've eliminated the possibility of it being the logic board as I replaced it already.