i power brake van and only rear wheels spin and now sense snow only rear spin where do i start thanks

The transfer case is a full-time overrunning clutch type. "Power-braking" may have "powerfully-broken" the sprag, or possibly even the chain in the NPG136, or a side gear in the front differential. You can get away with that on a RWD (usually) but not a 4WD/AWD without damage.

Raise the vehicle and support it on stands or a frame rack. Start and run it in drive and make sure both driveshafts are turning. That's the first step. If the shafts are both turning (specifically the front one) try restraining one of the front wheels (VERY carefully) and see if the opposite wheel spins faster or the driveshaft stops.

Either way, it's probably not going to be pretty when you find the damage.

The transfer case is a full-time overrunning clutch type. "Power-braking" may have "powerfully-broken" the sprag, or possibly even the chain in the NPG136, or a side gear in the front differential. You can get away with that on a RWD (usually) but not a 4WD/AWD without damage.

Raise the vehicle and support it on stands or a frame rack. Start and run it in drive and make sure both driveshafts are turning. That's the first step. If the shafts are both turning (specifically the front one) try restraining one of the front wheels (VERY carefully) and see if the opposite wheel spins faster or the driveshaft stops.

Either way, it's probably not going to be pretty when you find the damage.