Original post by: LikeARabbit ,
Did you ever remove or disconnect the Airport card during the LCD repair? My memory is a bit foggy on this but this sounds like a symptom we used to see when the cable inserted into the Airport card upside down. Immediately after shutting the Mac down it would power back on. One side of the cable's connection should have two small grounding tabs (like two small C's cut out), if these are visible and facing outward then this is likely the cause. Unfortunately I seem to recall irreversible damage being done to the logic board if this situation arose.