If it won't go into gear at all the transmission likely needs a rebuild and the main thing you need to ask yourself before you do that and be honest is do you NEED 4wd? Can you drive the car without it? If you don't NEED 4wd then it's not worth fixing unless you live in Russia or northern Canada even then you probably don't need it. You've already diagnosed this issue. If it won't go into gear at all it could be a NUMBER of different things wrong with it up to and including the transmission but we only know as much as you do and you'll have to take it to a mechanic you can trust to tell you what the damage is. It could be your drive shafts joint it broken or a few other things.... And here's how I would do the 4x4 fix math: how much is the car worth in roughly the condition its in with 4x4 fixed? If the repairs cost more than whatever that number is the repair is not worth the price of the vehicle and a waste of money.    

I completely agree with Jacksonishere.

It is an old car with I assume has lots of miles. Does not worth fixing the 4WD system.