I have a 1999 honda accord. Bought it and it ran and drove but had a bad head gasket. I drove it into the garage, took the head off and put it back on but now the car wont even crank. The shifter also wont shift out of park even with the battery in. Ive tried three different batteries knowing theyre all good batteries. Tried jumping the starter solenoid, sometimes it free spins without kicking out sometimes it doesnt spin at all. I also dont notice the "green key" light for the immobilizer. Trying to figure out if there might be a plug i forgot to plug in, or a bad ground, or what else it could be. What really hs me stumped is that the shifter wont even move out of park.

 

If the green key in the dash doesn't light up, it won't start. This is due to the immobilizer. This means that both the key and the ECU need to be reprogramed.
As for grounds to check, look for the G101 grounds on the end of the intake manifold, because if they're off, you'll get no key action start at all (green key or no green key). I only say that, since you've had the head off.