If you choose the Access Psionic Talent feat, you choose 5 psionic talents (which are 0-level psionic powers), then if you have enough power points to spend, you can activate "Precognition, Greater", then "Inertial Armor", then "Thicken Skin", then "Force field". Each of these add Armor Class modifiers and sometimes saving throw modifiers. Can they stack?
Well, let's look
- Precognition, Greater, is a power level 6 seer discipline. On the other hand, perhaps you meant Precognition, Defensive which does produces an insight bonus. It thus stacks with everything other than other insight bonuses.
- Inertial Armor provides an armor bonus. It thus stacks with everything other than other sources of armor. In particular, it will not stack with worn armor.
- Thicken Skin adds to natural armor, and thus stacks with everything
- Force Screen provides a shield bonus, and therefore does not stack with other things providing shield bonuses (like, say, physical shields), but stacks with everything else.
So, if you had all four of those disciplines and powered them up, they'd stack with each other, though they wouldn't stack with shield, worn armor, or insight bonus, and the total overall AC, while not terrible, wouldn't be all that good, given what you were sinking into it.
The real kicker, though, is that you appear to have misread the rules pretty badly. None of these are talents. At the same time, Unlocked Talent doesn't give you any talents. It gives you 2 power points (plus the 2 you got from Wild Talent) and a single 1st-level discipline. Further, Unlocked Talent is not one of the feats that you're specifically allowed to take multiple times.
Still, it seems like a feat that would be reasonable to take multiple times. I don't think it would break the game. Thus, if you convince your DM to houserule it, and you spend 5 feats getting Wild Talent followed by each of the four previously described powers, you could use them all at once, and they'd all add to your AC... with a result that would be deeply unimpressive for the level that you'd have to achieve to get that many feats to play with, and that you'd only be able to maintain for a short while before the power ran out.
First, there's a core gameplay question here: "Can different modifiers stack?" To answer that part, nothing about psionics is special when it comes to stacking. When different bonuses to the same statistic apply, you take the largest of each type. This means you can't gain the combined effect of two different shield bonuses, or two different insight bonuses, or two different bonuses from an ally using the 'aid another' action to help you. Some bonuses don't have a type, which means they stack, if they're from different sources. A bonus will never stack with an identical bonus. For example, if two of your teammates are valid flanking partners, you only gain the larger flanking bonus.
Second, there seems to be some confusion about the powers you're allowed to take with Access Psionic Talent. If your GM isn't giving you free rein, then you should only be selecting powers that appear as 0-level powers on some class power list.
For instance, lesser fortify is a 0-level power for cryptics, dreads, psions, wilders, psychic warriors, tacticians, gamblers and empaths, so you could learn it as one of your five Access Psionic Talent powers.
However, because thicken skin isn't a 0-level power on any class list, the only feats that let you learn it as a power are Unlocked Talent (thicken skin), Extra Power Known (thicken skin) for a class that has thicken skin on its power list, or Expanded Knowledge (thicken skin) for any other class.