[antonio112]

pawn Code:

CMD:locker(playerid, params[]) {
    if (IsPlayerInRangeOfPoint(playerid, 3, 770.6819,-77.5974,1000.6563) && GetPlayerInterior(playerid) == 7)
           ShowPlayerDialog(playerid,100,DIALOG_STYLE_LIST,"Locker Room.","Health Kit\t(Free)\nArmour\t(5)\nColt.45\t(4)\nDesertEagle\t(6)","Purchase","Exit");
    return 1;
}

All you had to do was to delete "!". "!" means is not. So, in your case, player IS NOT in range of point.