Engaged starter and all current went dead throughout the vehicle. Unhooked batter cables and had current coming from battery but everything dies when connecting cable back on starter. Engine cranks OK with hand crank so not jammed. Not good!
Starter bushings may be shot. Time to check it for rotation. It may also have e a short somewhere in there. This assumes that you've already checked the battery and cabling.
The poor mans battery load check is to turn lights on with someone watching intensity and then hit the starter pedal. If the lights dim out and the starter turns slowly then either there is no capacity in the battery or the cabling is going south. The starter is the last check. Battery and connection testing is the easier of the two and a person should always do the easy stuff first when troubleshooting.