1000watt does not equal a working pc it just means enough juice for almost anything (if it is not broken:P).
Check your wiring it might be that some wires got loose which are essential for the MB to start (use the manual to be sure).
If your pc is properly connected we move to the next step.
Next step would be if possible to try to test your mobo with another psu (without any add ons like hdd, dvd-player, gfx card etc.) and without the current psu attached with only the most essential wires and things like ram and case connected. If you have no other psu then still only the bare essentials without any add ons.
Still no good try to have the psu and or MB tested at a local pc shop.
If it does start up you can begin adding your old stuff (begin with gpu then hdd all the way to your current set up).
If it does not start up after you've plugged in something (like the gpu) you should post here again only then can we look at what might be the problem.
PS: obviously this should all be done after you've shutdown your pc and disconnected the psu from power.