Transmission will not go into reverse

Bought the vehicle listed above and a week later would not go into reverse and now will not shift gears. The people i bought it from said they had a new transfer-case put in a month prior to me buying it and after they got it home it was only driven a couple times but did not seem to have any problems. Do i need a new transmission now? My brother said that when they did the transfer-case that they may not have put enough fluid back in it? I am a female and know the basics on cars but not deep detail.