Can't draw spells (Arx Fatalis)

The first time barely did a spell of fire.Did not succeed to make the letter And now trying to make the fireball spell, but does not make a letter And sign of lightning.The first line goes, and then does not work, once is probably like that randomly happened, but is no longer worked. What can you recommend? On YouTube by the way looked and noticed that they have a line thinner than me.