MacBook Pro Won't power on at all!

This is a real odd one! My friend's MacBook Pro had a broken O key, so he took it apart to replace the keyboard, but didn't know how to put it together so he gave it to me. I meticulously reassembled the machine, and now it won't power on! When plugged in the green light comes on the magsafe charger, and the battery indicators light up fine. Then, the sleep light start s to fade in, but abruptly stops. If you listen very very closely you can hear the fan initiate then stop in time with the sleep light. Took it to the Apple store where the technician said he couldn't figure out what was wrong, but that everything seemed to be assembled correctly. Have already tried SMC and NVRAM resets to no avail.