In my opinion your best bet is to take a look at the service manual
and make sure you plugged everything back in. It should show all the cables and where they belong somewhere in the manual.
But first just try this since it sounds like you just forgot to reconnect the power button (I've done that countless times and it's always a relief finding out that's my problem and not something serious). If that's the case go to page 71 of that manual and it will show you where it connects and give you a general idea of how it connects. If that's not the problem let me know and i'll see if i can help anymore.