My first thought would be that it's something conlficting with Xfire, but that would suprise me as I also use Xfire, nonetheless try turning Xfire off before you start playing, check if you can use a skill.

Does the game crashes if you use skills before you start the initial cutscene between the human and the dwarf, or only after you have seen the cutscene?
Have you tried going to Verdistis, trying skills there, then coming back and try to use skills here?

Try a new game and see if you can use skills, maybe your save file's corrupt.

[Linked Image from miniprofile.xfire.com]