Was driving normally and without any warning I lost all power to wheels. car will not move forward or backward when engaged in drive or reverse.

check the trans fluid and filter, poor condition fluid could cause this type of thing

you might need a new whole transmission or new brakes or brake fluid.

drive wagon forward and backwards i:e change from 1st to reverse whilst trying to change to two wheel drive

My Econoline 250 with 4.2 lost fluid from hose leak, fixed leak everything was normal for 3 days till I drove it on highway. When it went into overdrive lost forward power. Turned off OD and did ok for a while. Lost forward gears slowly, put in fluid, hard to tell when full. Reverse is fine but have to rev up engine to get forward to engage, then everything is fine at lights and such till take out of drive, then have to rev engine to about 2500rpm to engage drive. Help?

torque converter

yor car has got the troublesome jatco gearbox. you need to get someone with a code reader to get the fault codes out of the tcm {transmission control module} may be just low fluid level or selector cable jgate problem but more than likely the box has failed and needs replaced/repaired

your i35 is a maxima

most 4x4s have to go in reverse to disengage from 4 wheel drive to 2 wheel drive.

Try reversing the car 2or3 times then go forward and try the box and see if it stays in then.
Let me know how you go Ron

With the selector in 2WD, attempt to slowly move the car forward (drive)and backward (reverse) in an area of 15 or 20 feet. That should release the 4WD gearing engagement.

Good luck
Aduz