Hmmm...
Did you check the other skill bars? You have five skill bars. Is it possible that you scrolled to an empty skill bar and didn't notice?
Also, it is possible to remove skills from the skill bar by dragging inventory items onto them, then dragging them out.
Press K to bring up your skill listing. The skill should still be there, and you can drag the icon back onto the skill bar.
By default the wizard does not have fire spells, but Flare and a one time use Fireball Scroll. The other default spells are Midnight Oil and Magical Poison Dart (you can change one of them to Burning Touch during character creation, though, in which case your use of the plural in spells would be correct).
The Staff of Magus spell will be blacked out if you changed to a non-staff type weapon.
Ah, thanks folks. I somehow moved the Flare and Poison Dart skill off the action bar. Thank you very much for pointing me in the right direction.