I've cast the first two spells (fire & frost) at the pillar but no matter which order I cast magicka damage or fortify, it fails. I have Denel's chest of scrolls but none seems to work.

Is there a trick to this, once past the first two?

Make sure you are casting them in the correct order: Fire, Frost, Damage Magicka, Fortify Magicka.

Yes, I've done that order a few times. It's the damage one that doesn't take, for some reason.

It seems I wasn't standing close enough to the pillar for the damage magicka spell to work. I went right up to it and it worked.

That one is an On Touch spell. The others are On Target.