Please help, why wont my 4 wheel drive work?

ok soi bought a 96 ford ranger xlt with 4-wheel drive and the guy said i have to turn the hubs to ''lock'' if iwant to use it because he said his son dissabled the ons on the dash that say 4 high and 4 low, which he might be lying about that. if i turn the hubs i hear like a click but not all 4 tires will spinjust the back ones do. and when i click it to free it actually clikcs in to place and when i click it to lock it just goes there it dont like click in, what could this be?!?!