Please Please help

[Sabre]

There is nothing wrong with your game, what happens is that you have reached the experience cap of the game. In Shadows of Amn, the maximum amount of experience a character can earn is 2,950,000 - this is total experience, not just for the current class.

In your case, a level 19 Fighter needs at least 2,750,000 xp, so you'll only have about 200,000 xp left for the Thief class. So you will not be able to get any more experience once you have got that 200,000 - which is after level 10, level 11 needs 220,000 experience points, which you won't be able to get.

[Littiz]

Apply the Xp-cap Remover and you'll be fine.
Or buy Throne of Bhaal, so the limit will be raised to 8,000,000