I'm not entirely sure where your numbers come from. I don't think you can get +5 damage from STR on a two-handed weapon. (+3 bonus goes to +4, +4 bonus goes to +6). If your STR bonus is +5 normally, using a two-handed weapon would make the bonus to damage +7.
And if this is a 1st level character, the Power Attack bonus to damage for using a two-handed weapon should be +3.
The general rule is that your weapon deals damage as follows:
Base Damage Die (or Dice) + STR Bonus + Power Attack Bonus
Since your weapon is a two-handed weapon, you actually get 1.5 STR and 1.5 Power Attack.
Assuming you have 20 Strength to start (for a +5 bonus to damage), use a Greatsword, and have Power Attack, your damage should look like this:
2d6 (base damage dice) + 7 (base of +5 times 1.5 rounded down) + 3 (power attack base is +2 times 1.5, again for using a two-handed weapon)
or
2d6 + 10
Even though a Greatsword rolls two dice for damage, the base damage of 2d6 is all one roll.
As fretgod says, you get your bonuses once per hit, not once per die of damage. He is also correct about multiplying bonuses with 2H weapons.
(Incidentally, 2H weapon users get the best result when their STR bonus is even, due to the rounding rules.)