2002 rodeo no gears?

So I changed out the oil on my rodeo, pulled the front end up on ramps to do it. drove it around the block, put in 4 wheel drive for pull just to make it easy to drive on ramps. when I was done it would not go into reverse, so I just gave it a little push to roll it off the ramps, it still wont grab any gears, the Trans fluid was changed about 15k miles ago, and looks to be at good level, I didn't knock anything around when I was under the vehicle... any help?

Are you sure transfer case is in 2wd high? Might try shifting it into 4wd or 4wd low and see if it will drive